Tenryū-ku (天竜区) is one of the three wards of the city of Hamamatsu, Shizuoka Prefecture, Japan.

It is bordered by Kita-ku and Hamakita-ku in Hamamatsu, the cities of Shimada and Iwata and towns of Mori and Kawanehon in Shizuoka, Shishiro, Tōei and Toyone in Aichi Prefecture and Iida and Tenryū in Nagano Prefecture.

It consists of five former cities, towns and villages, including the former city of Tenryū, and towns of Sakuma, Haruno and Misakubo that had previously merged into Hamamatsu on July 1, 2005.

It's heavily forested, contributing to forestry, which is one of the principal industries of Hamamatsu.

The average annual rainfall is 2,123.4 mm (83.60 in) with July as the wettest month.