| En Name: | Zainsk |
| Ru Name: | Заинск |
| Coordinates: | 55.3°N 53°W |
| Map Label Position: | right |
| Image Coa: | Coat of Arms of Zainsk (Tatarstan).png |
| Federal Subject: | Republic of Tatarstan |
| Adm City Jur: | town of republic significance of Zainsk |
| Adm Ctr Of1: | town of republic significance of Zainsk |
| Adm Ctr Of2: | Zainsky District |
| Inhabloc Cat: | Town |
| Mun District Jur: | Zainsky Municipal District |
| Urban Settlement Jur: | Zainsk Urban Settlement |
| Mun Admctr Of1: | Zainsky Municipal District |
| Mun Admctr Of2: | Zainsk Urban Settlement |
| Pop 2010Census: | 41803 |
| Established Date: | 1652–1656 |
| Current Cat Date: | 1978 |
Zainsk (ru|Заи́нск is a town in the Republic of Tatarstan, Russia, located on the Stepnoy Zay River (Kama's tributary), 287km (178miles) east of Kazan. Population: 39,739 (2021 census).[1]
Zainsk Reservoir, along the Zay River, is located near the town.
Within the framework of administrative divisions, Zainsk serves as the administrative center of Zainsky District, even though it is not a part of it.[2] As an administrative division, it is, together with the settlement of Karmalka, incorporated separately as the town of republic significance of Zainsk—an administrative unit with the status equal to that of the districts. As a municipal division, the town of republic significance of Zainsk is incorporated within Zainsky Municipal District as Zainsk Urban Settlement.[3]