State Route 378 (SR 378) is a 2-mile-long (3.2 km) state highway located in Dayton, Rhea County, in the U.S. state of Tennessee.

[2] SR 378 begins at an intersection with US 27/SR 60 and travels to the west, then marks a sharp turn and travels to the northeast toward Downtown Dayton.

In downtown, it has a brief 0.2-mile-long (0.32 km) concurrency with SR 30.

[2] SR 378 follows the former route of US 27 through downtown Dayton before the 4-lane bypass was built to the southeast.

The entire route is in Dayton, Rhea County.