| Tundzha Municipality | |
| Native Name: | Община Тунджа |
| Native Name Lang: | bg |
| Settlement Type: | Municipality |
| Coordinates: | 42.3167°N 55°W |
| Subdivision Type: | Country |
| Subdivision Type1: | Province |
| Subdivision Name1: | Yambol |
| Seat: | Yambol (outside the municipality) |
| Unit Pref: | Metric |
| Area Total Km2: | 1218.86 |
| Population Total: | 21435 |
| Population As Of: | 2019 |
| Population Density Km2: | auto |
Tundzha Municipality (Bulgarian: община Тунджа) is a municipality of Yambol Province, southeastern Bulgaria. The municipality has an area of 1,218.86 square kilometres, making it the second-largest by area in the country after the Capital Municipality (i.e. the city of Sofia). It covers 44 villages and has a population of 21,435 according to 2005 data. All the villages in the province are administratively equal, and the administrative centre of the municipality is located in the provincial capital of Yambol, which is not part of Tundzha municipality itself: the city is equivalent to Yambol Municipality, which is an enclave within Tundzha Municipality. Tundzha municipality is named after the Tundzha River, the most significant tributary of the Maritsa.
The following villages are part of Tundzha Municipality:
A notable native is Ivan Atanasov, the father of John Vincent Atanasoff (1903–1995), Bulgarian American physicist and inventor of the first automatic electronic digital computer. He was born in Boyadzhik. The Bezmer Air Base, one of the joint US-Bulgarian military bases, is also located in the municipality, near the villages of Bezmer and Bolyarsko.
According to the latest Bulgarian census of 2011, the religious composition, among those who answered the optional question on religious identification, was the following: