| Nansio | |
| Native Name: | Kata ya Nansio |
| Native Name Lang: | sw |
| Nickname: | Lake island town |
| Settlement Type: | Ward |
| Pushpin Map: | Tanzania#Africa |
| Pushpin Relief: | yes |
| Coordinates: | -2.1078°N 33.0864°W |
| Subdivision Type: | Country |
| Subdivision Type1: | Region |
| Subdivision Name1: | Mwanza Region |
| Subdivision Type2: | District |
| Subdivision Name2: | Ukerewe District |
| Subdivision Type3: | Ward |
| Subdivision Name3: | Nansio |
| Population As Of: | 2016 |
| Population Total: | 8,644 |
| Postal Code: | 33601 |
| Postal Code Type: | Postcode |
| Timezone: | EAT |
| Utc Offset: | +3 |
| Blank Name: | UFI |
| Blank Info: | -2571388 |
Nansio is a small Tanzanian port town and capital of Ukerewe District in Mwanza Region. The town is also a ward on the island of Ukerewe, Lake Victoria, in Tanzanian lake territory. Nansio is a port of entry for passenger and freight shipping services from the city of Mwanza.
The ward of Nansio is one of twenty-four in the district of Ukerewe. In 2016 the Tanzania National Bureau of Statistics reported there were 8,644 people in the ward, up from 7,674 in 2012.
The ward has 15 villages.