The Rhondda West by-election, 1920 was a parliamentary by-election held on 21 December 1920 for the British House of Commons constituency of Rhondda West in Wales. The seat had become vacant when the constituency's Labour Member of Parliament (MP), William Abraham, resigned from Parliament. He had held the seat since its creation at the 1918 general election, when he was returned unopposed. He had been the MP for the previous Rhondda constituency from its creation for the 1885 general election.