The 1998 United States Senate elections were held on November 3, 1998, with the 34 seats of Class 3 contested in regular elections. This was seen as an even contest between the Republican Party and Democratic Party. While the Democrats had to defend more seats up for election, Republican attacks on the morality of President Bill Clinton failed to connect with voters and anticipated Republican gains did not materialize. The Republicans picked open seats up in Ohio and Kentucky and narrowly defeated Democratic incumbent Carol Moseley Braun (Illinois), but these were cancelled out by the Democrats' gain of an open seat in Indiana and defeats of Republican Senators Al D'Amato (New York) and Lauch Faircloth (North Carolina). The balance of the Senate remained unchanged at 55–45 in favor of the Republicans, thereby tying these election results with those of 1996 and 2004 as the highest number of Senate seats that the Republicans have held since 1920.
This is the last election cycle that resulted in no net change in the balance of power and the last time Democrats won a U.S. Senate race in South Carolina. As of 2026, this is the most recent time in which the Democratic Party won a majority of Class 3 Senate seats in a regularly scheduled election.
Results summary
{| style="width:50em; text-align:center;"
|+ ↓
|- style="color:white;"
| style="background:; width:45%;" | 45
| style="background:; width:55%;" | 55
|-
| <span style="color:;">Democratic</span>
| <span style="color:;">Republican</span>
|}
{| class=wikitable style=text-align:center
|- valign=bottom
! rowspan=2 colspan=3 | Parties
| style="background-color:" |
| style="background-color:" |
| style="background-color:" |
| style="background-color:" |
! rowspan=2 | Total
|- valign=bottom
! Democratic
! Republican
! Libertarian
! Other
|-
! colspan=3 | Last elections (1996)<br/>Before the elections
| 45
| | 55
| 0
| 0
! 100
|-
! colspan=3 style="background:#bbb" | Not up
| 27
| | 39
| —
| —
! 66
|-
| colspan=100 |
|-
! colspan=3 style="background:#bbb" | Up<br/>
| | 18
| 16
| —
| —
! 34
|-
! rowspan=18 style="background:#bbb" | <!-- Gap for "Up"-->
|-
| colspan=100 |
|-
! colspan=2 style="background:#ccc" | Incumbent retired
| | 3
| 2
| —
| —
! 5
|-
! rowspan=3 |
!
| 1
| 1
| —
| —
! 2
|-
!
| colspan=2 | 1 Republican replaced by 1 Democrat<!--IN--><br/>2 Democrats replaced by 2 Republicans<!--KY, OH-->
| —
| —
! 3
|-
! Result
! 2
! | 3
! —
! —
! 5
|-
! colspan=2 style="background:#ccc" | Incumbent ran
| | 15
| 14
| —
| —
! 29
|-
! rowspan=4 |
!
| | 14
| 12
| —
| —
! 26
|-
!
| colspan=2 | 2 Republicans replaced by 2 Democrats<!--NY, NC--><br/>1 Democrat replaced by 1 Republican<!--IL-->
| —
| —
! 3
|-
!
| 0
| 0
| —
| —
! 0
|-
! Result
! | 16
! 13
! —
! —
! 29
|-
| colspan=100 |
|-
! colspan=2 | Total elected
| | 18
| 16
! 0
! 0
! 34
|-
! colspan=2 | Net gain/loss
|
|
|
|
! 0
|-
! colspan=2 style="background:#ccc" | Nationwide vote
| | 26,768,699
| 25,346,613
| 419,452
| 1,580,287
! 54,115,051
|-
! <!-- Gap for "Nationwide vote" -->
! Share
| | 49.47%
| 46.84%
| 0.78%
| 2.92%
! 100%
|-
! colspan=2 | Result
! 45
! | 55
! —
! —
! 100
|}
Source: Office of the Clerk
Alaska
Incumbent Republican Frank Murkowski easily won re-election to a fourth term against Democratic nominee Joseph Sonneman, a perennial candidate, earning nearly 75% of the vote.
Arizona
Incumbent Republican John McCain won re-election to a third term over Democratic attorney Ed Ranger.
California
Incumbent Democrat Barbara Boxer won re-election to a second term.
Although the race was predicted to be fairly close, Boxer still defeated Fong by a ten-point margin. Boxer as expected did very well in Los Angeles County, and the San Francisco Bay Area.