| Unit Name: | 21st Serbian Division |
| Dates: | 1944–1945 |
| Country: | Democratic Federal Yugoslavia |
| Branch: | Yugoslav Partisan Army |
| Type: | Infantry |
| Size: | ~1,000 (upon formation) |
| Battles: | World War II in Yugoslavia |
| Notable Commanders: | Miloje Milojević |
The 21st Assault Serbian Division (Serbo-Croatian Latin: Dvadesetprva udarna srpska divizija) was a Yugoslav Partisan division formed on Radan mountain on 20 May 1944. It was formed as 1st Serbia Division, but it was renamed on 14 June 1944.[1] Upon formation it had around 1,000 soldiers in three brigades, those being: the 4th, 5th and 6th Serbia Divisions.[2] Commander of the division was Miloje Milojević. The division mostly fought against Chetniks and Germans in occupied Serbia.