thumb|A bust of August Cesarec in [[Tkalčićeva Street, Zagreb]]
August Cesarec (4 December 1893 – 17 July 1941) was a Croatian writer and communist activist from the interwar period.
Cesarec was born in Zagreb, then part of Austria-Hungary. He was the son of a carpenter who was a member of the Social Democratic Party, and August himself published a short story in the party's magazine as early as 1910. As a high-school student he became involved in radical nationalist politics and joined the group that tried to assassinate Croatian ban (viceroy) Slavko Cuvaj in 1912. He then went to Paris, and in 1938 returned to Yugoslavia, where he was arrested at the border again.
Cesarec was a known polemicist, having contributed to Plamen, Borba, Književna republika, Komunista, Zaštita čovjeka, Nova riječ and Izraz.
He often argued for Marxist points of view, having redacted and prepared for print the Serbo-Croatian translation of Das Kapital made by Moše Pijade and Rodoljub Čolaković. At the same time, Cesarec advocated for the Croatian peasant movements led by Stjepan Radić, against Greater Serbian hegemony, and was one of the first people at the time to publicly recognize the Macedonians as a nation. He was also one of the first people among his contemporaries in Yugoslavia to write about Adler's individual psychology. Another one of the topics he was known for was arguing against the regressive nature of fascism and evaluating the work of Ante Starčević and Eugen Kvaternik as revolutionaries and against the clerical and Frankist (far-right) interpretations. As World War II started in Europe, he provided insightful analysis of world events and predicted the demise of the Molotov–Ribbentrop Pact.
In March 1941, a few days before the Axis invasion of Yugoslavia, he was arrested and interned in Kerestinec prison in Croatia, together with some 90 leading members of the Croatian left-wing intelligentsia. A few weeks later the prison was taken over by the new Ustasha regime.