State Route 403 (SR 403, now known as the Altoona–Pillar Rock Road) was a state highway in Wahkiakum County, in the U.S. state of Washington. It extended 10.4 miles (16.7 km) from Pillar Rock northwest to SR 4 in Rosburg. The route served as a connector to Pillar Rock. The highway was (SSH 12C) from 1943 until 1964, which ran from Pillar Rock to Rosburg. In 1991, SR 403 was removed from the state highway system.