Oscar Fredrik von Sydow (12 July 1873 – 19 August 1936) was a Swedish politician who served briefly as Prime Minister of Sweden from 23 February to 13 October 1921.

In the governments of Hjalmar Hammarskjöld and Carl Swartz (1914–1917) he was Minister for Civil Service Affairs, during which time he established the Unemployment Commission (arbetslöshetskommissionen).

Following the sudden resignation of the Prime Minister Louis De Geer in 1921, the King had difficulties finding a candidate willing to form a new government, as the elections were drawing near.

Hjalmar Branting declined, after being asked twice to become Prime Minister, and the appointment was offered to Oscar von Sydow, who accepted and took office on 23 February.

Von Sydow gave an ultimatum that he would not lead a powerless government and demanded that the Social Democratic Party promise to support him in important finance and defence issues.