The men's 100 metre butterfly event at the 2004 Olympic Games was contested at the Olympic Aquatic Centre of the Athens Olympic Sports Complex in Athens, Greece on August 19 and 20.
U.S. swimmer Michael Phelps broke an Olympic record of 51.25 to claim his fifth gold medal, edging out his teammate and world record holder Ian Crocker by four hundredths of a second (0.04). Meanwhile, Ukraine's Andriy Serdinov earned a bronze in a European record of 51.36. Earlier in the semifinals, Serdinov blasted a new Olympic record, previously set by Australia's Geoff Huegill in Sydney four years ago, with a time of 51.74. One heat later, Phelps stopped the clock at 51.61 to lower the record by 0.13 of a second.
Records
Prior to this competition, the existing world and Olympic records were as follows.
The following new world and Olympic records were set during this competition.
{| class=wikitable style=text-align:center
|-
! Date !! Event !! Name !! Nationality !! Time !! Record
|-
| August 19 || Semifinal 1 || Andriy Serdinov || align=left | || 51.74 ||
|-
| August 19 || Semifinal 2 || Michael Phelps || align=left | || 51.61 ||
|-
| August 20 || Final || Michael Phelps || align=left | || 51.25 ||
|}
Results
Heats
{| class="wikitable sortable" style="text-align:center"
|-
! Rank !! Heat !! Lane !! Name !! Nationality !! Time !! Notes
|-bgcolor=#ccffcc
| 1 || 8 || 4 ||align=left| Ian Crocker ||align=left| || 52.03 || Q
|-bgcolor=#ccffcc
| 2 || 6 || 4 ||align=left| Andriy Serdinov ||align=left| || 52.05 || Q
|-bgcolor=#ccffcc
| 3 || 7 || 4 ||align=left| Michael Phelps ||align=left| || 52.35 || Q
|-bgcolor=#ccffcc
| 4 || 5 || 4 ||align=left| Milorad Čavić ||align=left| || 52.44 || Q
|-bgcolor=#ccffcc
| 5 || 7 || 7 ||align=left| Geoff Huegill ||align=left| || 52.54 || Q
|-bgcolor=#ccffcc
| 6 || 7 || 1 ||align=left| Duje Draganja ||align=left| || 52.56 || Q
|-bgcolor=#ccffcc
| 7 || 7 || 5 ||align=left| Thomas Rupprath ||align=left| || 52.57 || Q
|-bgcolor=#ccffcc
| 8 || 8 || 3 ||align=left| Franck Esposito ||align=left| || 52.61 || Q
|-bgcolor=#ccffcc
| 9 || 8 || 5 ||align=left| Igor Marchenko ||align=left| || 52.62 || Q
|-bgcolor=#ccffcc
| 10 || 7 || 6 ||align=left| Takashi Yamamoto ||align=left| || 52.71 || Q
|-bgcolor=#ccffcc
| 11 || 8 || 2 ||align=left| Gabriel Mangabeira ||align=left| || 52.76 || Q
|-bgcolor=#ccffcc
| 12 || 7 || 2 ||align=left| James Hickman ||align=left| || 52.91 || Q
|-bgcolor=#ccffcc
| 13 || 6 || 3 ||align=left| Yevgeny Korotyshkin ||align=left| || 52.93 || Q
|-bgcolor=#ccffcc
| 14 || 8 || 6 ||align=left| Mike Mintenko ||align=left| || 52.96 || Q
|-bgcolor=#ccffcc
| 15 || 7 || 3 ||align=left| Corney Swanepoel ||align=left| || 53.07 || Q
|-bgcolor=#ccffcc
| 16 || 8 || 7 ||align=left| Helge Meeuw ||align=left| || 53.11 || Q
|-
| 17 || 8 || 8 ||align=left| Kaio Almeida ||align=left| || 53.22 ||
|-
| 18 || 5 || 1 ||align=left| Ryan Pini ||align=left| || 53.26 ||
|-
| 19 || 6 || 6 ||align=left| Joris Keizer ||align=left| || 53.41 ||
|-
| 20 || 8 || 1 ||align=left| Adam Pine ||align=left| || 53.45 ||
|-
| 21 || 6 || 2 ||align=left| Denys Sylantyev ||align=left| || 53.46 ||
|-
| 22 || 6 || 5 ||align=left| Todd Cooper ||align=left| || 53.48 ||
|-
| 23 || 6 || 1 ||align=left| Mattia Nalesso ||align=left| || 53.49 ||
|-
| 24 || 5 || 7 ||align=left| Simão Morgado ||align=left| || 53.53 ||
|-
| 25 || 5 || 5 ||align=left| Frederick Bousquet ||align=left| || 53.63 ||
|-
| 26 || 5 || 6 ||align=left| Pavel Lagoun ||align=left| || 53.87 ||
|-
| 27 || 7 || 8 ||align=left| Ioan Gherghel ||align=left| || 53.89 ||
|-
| 28 || 4 || 4 ||align=left| Jere Hård ||align=left| || 54.02 ||
|-
| 29 || 4 || 6 ||align=left| Peter Mankoč ||align=left| || 54.14 ||
|-
| 30 || 6 || 8 ||align=left| Eugene Botes ||align=left| || 54.15 ||
|-
| 31 || 4 || 5 ||align=left| Sotirios Pastras ||align=left| || 54.20 ||
|-
| 32 || 5 || 2 ||align=left| Erik Andersson ||align=left| || 54.26 ||
|-
| 33 || 6 || 7 ||align=left| Joshua Ilika Brenner ||align=left| || 54.29 ||
|-
| 34 || 5 || 3 ||align=left| Zsolt Gáspár ||align=left| || 54.43 ||
|-
| 35 || 4 || 1 ||align=left| Rimvydas Šalčius ||align=left| || 54.46 ||
|-
| 36 || 5 || 8 ||align=left| Luis Rojas ||align=left| || 54.58 ||
|-
| 37 || 4 || 2 ||align=left| Camilo Becerra ||align=left| || 54.71 ||
|-
| 38 || 3 || 5 ||align=left| Jeong Doo-hee ||align=left| || 54.76 ||
|-
| 39 || 2 || 3 ||align=left| Michal Rubáček ||align=left| || 54.87 ||
|-
| 40 || 4 || 7 ||align=left| Georgi Palazov ||align=left| || 54.91 ||
|-
| 41 || 3 || 7 ||align=left| Rustam Khudiyev ||align=left| || 55.03 ||
|-
| 42 || 3 || 2 ||align=left| Hjörtur Már Reynisson ||align=left| || 55.12 ||
|-
| 43 || 4 || 3 ||align=left| Wu Peng ||align=left| || 55.17 ||
|-
| 44 || 3 || 4 ||align=left| Eduardo Germán Otero ||align=left| || 55.24 ||
|-
| 45 || 3 || 3 ||align=left| Aleksandar Miladinovski ||align=left| || 55.71 ||
|-
| 46 || 2 || 6 ||align=left| Oleg Lyashko ||align=left| || 55.90 ||
|-
| 47 || 3 || 1 ||align=left| Juan Pablo Valdivieso ||align=left| || 55.98 ||
|-
| 48 || 3 || 6 ||align=left| Aghiles Slimani ||align=left| || 56.22 ||
|-
| 49 || 3 || 8 ||align=left| Onur Uras ||align=left| || 56.37 ||
|-
| 50 || 2 || 5 ||align=left| Nicholas Rees ||align=left| || 56.39 ||
|-
| 51 || 2 || 8 ||align=left| Gordon Touw Ngie Tjouw ||align=left| || 56.68 ||
|-
| 52 || 2 || 2 ||align=left| Conrad Francis ||align=left| || 56.80 ||
|-
| 53 || 4 || 8 ||align=left| Andrejs Dūda ||align=left| || 56.81 ||
|-
| 54 || 2 || 4 ||align=left| Andy Wibowo ||align=left| || 56.86 ||
|-
| 55 || 2 || 7 ||align=left| Daniel O'Keeffe ||align=left| || 57.39 ||
|-
| 56 || 2 || 1 ||align=left| Davy Bisslik ||align=left| || 57.85 ||
|-
| 57 || 1 || 5 ||align=left| Luis Matias ||align=left| || 58.92 ||
|-
| 58 || 1 || 4 ||align=left| Fernando Medrano Medina ||align=left| || 1:00.91 ||
|-
| 59 || 1 || 3 ||align=left| Rad Aweisat ||align=left| || 1:01.60 ||
|}
Semifinals
Semifinal 1
{| class="wikitable sortable" style="text-align:center"
|-
! Rank !! Lane !! Name !! Nationality !! Time !! Notes
|-bgcolor=#ccffcc
| 1 || 4 ||align=left| Andriy Serdinov ||align=left| || 51.74 || Q,
|-bgcolor=#ccffcc
| 2 || 3 ||align=left| Duje Draganja ||align=left| || 52.74 || Q
|-
| 3 || 2 ||align=left| Takashi Yamamoto ||align=left| || 52.81 ||
|-
| 4 || 6 ||align=left| Franck Esposito ||align=left| || 52.88 ||
|-
| 5 || 1 ||align=left| Mike Mintenko ||align=left| || 52.89 ||
|-
| 6 || 8 ||align=left| Helge Meeuw ||align=left| || 52.99 ||
|-
| 7 || 7 ||align=left| James Hickman ||align=left| || 53.10 ||
|-
| 8 || 5 ||align=left| Milorad Čavić ||align=left| || 53.12 ||
|}
Semifinal 2
{| class="wikitable sortable" style="text-align:center"
|-
! Rank !! Lane !! Name !! Nationality !! Time !! Notes
|-bgcolor=#ccffcc
| 1 || 5 ||align=left| Michael Phelps ||align=left| || 51.61 || Q,
|-bgcolor=#ccffcc
| 2 || 4 ||align=left| Ian Crocker ||align=left| || 51.83 || Q
|-bgcolor=#ccffcc
| 3 || 2 ||align=left| Igor Marchenko ||align=left| || 52.32 || Q
|-bgcolor=#ccffcc
| 4 || 7 ||align=left| Gabriel Mangabeira ||align=left| || 52.33 || Q
|-bgcolor=#ccffcc
| 5 || 3 ||align=left| Geoff Huegill ||align=left| || 52.64 || Q
|-bgcolor=#ccffcc
| 6 || 6 ||align=left| Thomas Rupprath ||align=left| || 52.71 || Q
|-
| 7 || 1 ||align=left| Yevgeny Korotyshkin ||align=left| || 52.85 ||
|-
| 8 || 8 ||align=left| Corney Swanepoel ||align=left| || 52.99 ||
|}
Final
{| class="wikitable sortable" style="text-align:center"
|-
! Rank !! Lane !! Name !! Nationality !! Time !! Notes
|-
| || 4 ||align=left| Michael Phelps ||align=left| || 51.25 ||
|-
| || 3 ||align=left| Ian Crocker ||align=left| || 51.29 ||
|-
| || 5 ||align=left| Andriy Serdinov ||align=left| || 51.36 || EU
|-
| 4 || 1 ||align=left| Thomas Rupprath ||align=left| || 52.27 ||
|-
| 5 || 6 ||align=left| Igor Marchenko ||align=left| || 52.32 ||
|-
| 6 || 2 ||align=left| Gabriel Mangabeira ||align=left| || 52.34 ||
|-
| 7 || 8 ||align=left| Duje Draganja ||align=left| || 52.46 ||
|-
| 8 || 7 ||align=left| Geoff Huegill ||align=left| || 52.56 ||
|}