State Route 45 (SR 45) is a state highway in the U.S. State of California that travels in a north–south direction from Route 113 in Knights Landing to Route 32 in Hamilton City.

This route is part of the California Freeway and Expressway System.

The route begins at SR 113 in Knights Landing in Yolo County. It then heads northward and enters Colusa County, where it has a short overlap with SR 20. It then enters Glenn County, where it overlaps SR 162 through the cities of Codora and Glenn. It the continues northward to its end at SR 32 in Hamilton City.

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 numbers reset at county lines; the start and end postmiles in each county are given in the county column.