| Election Name: | 1921 Southwark South East by-election |
| Type: | presidential |
| Country: | United Kingdom |
| Previous Election: | Southwark South East (UK Parliament constituency)#Elections in the 1910s |
| Previous Year: | 1918 |
| Next Election: | Southwark South East (UK Parliament constituency)#Elections in the 1920s |
| Next Year: | 1922 |
| Election Date: | 14 December 1921 |
| Candidate1: | Naylor |
| Party1: | Labour Party (UK) |
| Popular Vote1: | 6,561 |
| Percentage1: | 57.0 |
| Candidate2: | Jacobsen |
| Party2: | Coalition Liberal |
| Popular Vote2: | 2,636 |
| Percentage2: | 22.9 |
| Candidate3: | Boot |
| Party3: | Independent Conservative |
| Popular Vote3: | 2,307 |
| Percentage3: | 20.1 |
| Map Size: | 250px |
| MP | |
| Posttitle: | Subsequent MP |
| Before Election: | Dawes |
| Before Party: | Liberal Party (UK) |
| After Election: | Naylor |
| After Party: | Labour Party (UK) |
The 1921 Southwark South East by-election was a parliamentary by-election held on 14 December 1921 for the British House of Commons constituency of Southwark South East, in the Metropolitan Borough of Southwark in London.
The seat had become vacant on the death of the constituency's Coalition Liberal Member of Parliament (MP), James Arthur Dawes. Dawes had been MP for Southwark South East since the 1918 election, and before that Walworth since the January 1910 election.