| Unit Name: | Japanese Twenty-First Army |
| Dates: | September 19, 1938 - February 19, 1940 |
| Country: | Empire of Japan |
| Branch: | Imperial Japanese Army |
| Type: | Infantry |
| Role: | Corps |
| Garrison: | Guangzhou |
| Nickname: | none |
| Battles: | Canton Operation |
The was an army of the Imperial Japanese Army during the Second Sino-Japanese War.
The Japanese 21st Army was formed on September 19, 1938 under the Imperial General Headquarters. It was transferred to the control of the China Expeditionary Army on September 23, 1939 and assigned the primary role in the Canton Operation (the invasion of Guangdong Province in southern China), together with the Imperial Japanese Navy’s 5th Fleet.
On October 12, the 18th and 104th Divisions landed, followed by command units the following day. By October 21, the provincial capital of Guangzhou was under Japanese control. The IJA 5th Division continued to advance up the Pearl River and by November 5 had taken the city of Foshan. By the end of November, the entire province was under Japanese control.
The Japanese 21st Army was disbanded on February 9, 1940. Its command staff joined the staff of the Japanese Southern China Area Army, and its divisions were reassigned to other areas.
| Name | From | To | |
| 1 | 8 September 1938 | 9 November 1938 | |
| 2 | 9 November 1938 | 10 February 1940 | |
| Name | From | To | |
| 1 | 8 September 1938 | 1 August 1939 | |
| 2 | 1 August 1939 | 1 December 1939 | |
| 3 | 1 December 1939 | 10 February 1940 | |
21st Army