The accident happened Saturday just after 2:30 p.m. at the intersection of Westlake Boulevard and Bay Drive.
The motorcyclist was identified as 39-year-old Christian Eitelbach of Thousand Oaks. Authorities say he was heading northbound on Westlake Boulevard and entered the intersection as 21-year-old Cindy Nah, of Simi Valley, was making a left turn. That's when the two collided.
Eitelbach and Nah were both treated at the scene before being transported to Los Robles Hospital. Eitelbach was pronounced dead at the hospital. Nah was treated for minor injuries.
The cause of the accident is under investigation. Anyone with information is asked to call the Thousand Oaks Traffic Bureau at (805) 494-8271.