State Route 263 (SR 263) is a state highway in the U.S. state of California in Siskiyou County. It is also part of Business Loop 5 due to being a parallel route of Interstate 5 to the west. Route 263 connects Route 3 near the north city limits of Yreka to Route 96 eight miles (13 km) north. It was once part of U.S. Route 99.

The road begins at a junction with State Route 3 just north of Yreka. The highway then heads upward through Siskiyou County, roughly lying parallel to the Klamath River. The road passes also roughly aligned with nearby Interstate 5 as it passes through hilly terrain. The road ends at State Route 96, which continues northward to meet up with Interstate 5.

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 Siskiyou County.