| State: | CA |
| Type: | SR |
| Route: | 45 |
| Section: | 345 |
| Maint: | Caltrans |
| Map Notes: | SR 45 highlighted in red |
| Length Mi: | 70 |
| Length Round: | 0 |
| Established: | 1934 |
| Direction A: | South |
| Terminus A: | at Knights Landing |
| Junction: | |
| Direction B: | North |
| Terminus B: | at Hamilton City |
| Counties: | Yolo, Colusa, Glenn |
| Previous Type: | SR |
| Previous Route: | 44 |
| Next Type: | SR |
| Next Route: | 46 |
State Route 45 (SR 45) is a state highway in the U.S. State of California that travels in a north - south direction in the Sacramento Valley from Route 113 in Knights Landing to Route 32 in Hamilton City.
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 then continues northward to its end at SR 32 in Hamilton City.
SR 45 is part of the California Freeway and Expressway System, but is not part of the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration.