State Route 172 (SR 172) is a state highway in the U.S. state of California in Tehama County. It is a loop route off of State Route 36.

SR 172 begins at a junction with SR 36 and heads southeast through Lassen National Forest. The route then turns south, crossing the South Fork Battle Creek and entering a wooded area. The road then winds eastward through the forest, roughly parallel to the Mill Creek. SR 172 then turns northward along Mill Creek and heads back toward SR 36, its eastern terminus.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in Tehama County.