| Country: | New South Wales |
| Type: | parliamentary |
| Ongoing: | no |
| Election Date: | 10 December 1921 |
| Vote Type: | Popular |
| Image1: | Herbert Pratten - May Moore (cropped).jpg |
| Candidate1: | Herbert Pratten |
| Party1: | Nationalist Party (Australia) |
| Popular Vote1: | 20,768 |
| Percentage1: | 66.0% |
| Swing1: | 6.6pp |
| Candidate2: | William Hutchison |
| Party2: | Australian Labor Party |
| Popular Vote2: | 5,625 |
| Percentage2: | 17.9% |
| Swing2: | 9.5pp |
| MP | |
| Before Election: | Joseph Cook |
| Before Party: | Nationalist Party (Australia) |
| After Election: | Herbert Pratten |
| After Party: | Nationalist Party (Australia) |
| Election Name: | 1921 Parramatta by-election |
| 1Data2: | 26.0% |
| 2Blank: | TPP swing |
| 2Data1: | 3.4pp |
| 2Data2: | 3.4pp |
| 1Data1: | 76.0% |
| 1Blank: | TPP |
A by-election was held for the Australian House of Representatives seat of Parramatta on 10 December 1921. This was triggered by the resignation of Nationalist MP, Treasurer and former Prime Minister Sir Joseph Cook to become Australian High Commissioner to the United Kingdom.
The by-election was won by Nationalist candidate Herbert Pratten, who resigned from the Senate to run.