| Conflict: | Battle of Lạng Sơn |
| Place: | Lạng Sơn, French Indochina |
| Partof: | Japanese invasion of French Indochina |
| Date: | 22–25 September 1940 |
| Result: | Japanese victory |
| Territory: | Capture of Lạng Sơn, withdraw of French forces to Thái Nguyên[1] |
| Combatant1: |
|
| Units2: | 5th Foreign Infantry Regiment French colonial troops |
| Coordinates: | 21.8478°N 106.7578°W |
| Units1: | Imperial Japanese 5th Division |
| Strength1: | >5,000 |
| Strength2: | ~5,000[2] |
| Commander1: | Aketo Nakamura |
| Commander2: | Germain Mennerat |
The Battle of Lạng Sơn (1940) was a short military battle between Imperial Japan and Vichy France in French Indochina. This battle was one of the very few battles of the Japanese invasion of French Indochina, an invasion only lasting three days.
This battle took place in Lạng Sơn, and the areas surrounding it, which are located in modern-day northern Vietnam.The city was invaded by the Japanese army, after forcibly crossing the Chinese border into Vietnam.[3] The French forces were outnumbered by Japan's forces,[4] and they were forced to withdraw from the city on 25 September 1940, where they retreated to Thái Nguyên.[5]