The Kubnya (Кубня, Кĕтне, ) is a river in Chuvashia and Tatarstan, Russian Federation, a left-bank tributary of the Sviyaga River. It's length is 176 km (121 of them in Tatarstan) and its drainage basin is 2,480 km². It origins in Chuvashia and falls to the Sviyaga River 4 km south of Burunduki.
Major tributary is Uryum River. The maximal mineralization is 500-800 mg/l. Average sediment in mouth per year is 92 mm. The maximal water discharge is 420 m³/s. Drainage is regulated. Since 1978 it is protected as natural monument of Tatarstan.