KOST (103.5 FM, KOST 103.5) is a radio station licensed to Los Angeles, California, with a Mainstream AC musical format. It is one of three Adult Contemporary-based formatted radio station in the Los Angeles/Orange County area, the others being sister station KBIG (Hot AC) and CBS-owned Smooth/Urban AC KTWV. The station is one of the top rated radio stations in Los Angeles and one of the top revenue billing radio stations in the United States. According to the radio industry website, RadioStats.Net] KOST's site is the most visited Adult Contemporary radio station website in America. KOST also has translators at 103.9 FM in Thousand Oaks, CA and at 105.5 in Ridgecrest, CA.

Kost or KOST may refer to:

• KOST, a radio station (103.5 FM) licensed to Los Angeles, California, United States
• Kost Castle, a castle in Czech Republic
• Kost, Minnesota, a community in the United States