| Club: | Chelsea |
| Season: | 1920–21 |
| Manager: | David Calderhead |
| Chairman: | Claude Kirby |
| Stadium: | Stamford Bridge |
| League: | First Division |
| League Result: | 18th |
| Cup1: | FA Cup |
| Cup1 Result: | Quarter-finals |
| League Topscorer: | Jack Cock (12) |
| Season Topscorer: | Jack Cock (15) |
| Largest Win: | 5–1 v Aston Villa |
| Largest Loss: | 0–5 v Tottenham Hotspur |
| Highest Attendance: | |
| Lowest Attendance: | |
| Pattern B1: | _chelsea1907h |
| Pattern So1: | _2bluestripes |
| Leftarm1: | 0000FF |
| Body1: | FFFFFF |
| Rightarm1: | 0000FF |
| Shorts1: | ffffFF |
| Socks1: | 000000 |
| Pattern B2: | _chelsea1905a |
| Pattern So2: | _2_stripes_white |
| Leftarm2: | FFFFFF |
| Body2: | FFFFFF |
| Rightarm2: | FFFFFF |
| Shorts2: | FFFFFF |
| Socks2: | 0000ff |
| Prevseason: | 1919–20 |
| Nextseason: | 1921–22 |
The 1920–21 season was Chelsea Football Club's twelfth competitive season.