The bus driver and eight passengers also were injured in the 2 a.m. crash on Highway 101 at Burlingame, the San Francisco Chronicle reported.
The California Highway Patrol said the unidentified 36-year-old woman who died was a passenger in a car driven by her 43-year-old husband, Raul Padilla of Oakland. Their southbound car went out of control for an unknown reason and came to a stop in the two left lanes facing north.
The southbound party bus then struck the front of the car, the Highway Patrol said. Two other cars were involved in the crash.
Authorities said the couple in the car had been drinking but it was unknown what role, if any, it played in the crash.