Sihanouk International Airport (formerly Sihanoukville International Airport; ) , located east of Sihanoukville City in Sihanoukville Province, is Cambodia's third largest international airport. It is named, like the province itself, after King Norodom Sihanouk. The airport is also known as Kang Keng Airport (). The IATA code KOS is derived from Sihanoukville's alternative name, "Kampong Som".
The airfield was originally constructed in the 1960s with assistance from the Soviet Union. After a long period of dormancy during and after the Khmer Rouge era, the airport formally reopened on 5 January 2007. The runway was extended to a length of in order to accommodate 4E class aircraft. The 2 existing taxiways were widened and a cargo apron for 4E class aircraft was added. However, after the crash of PMTair Flight U4 241 in June 2007 shortly before landing, scheduled passenger flight service to the airport was discontinued until 2011.
Cambodia Angkor Air started a tri-weekly service from Angkor International Airport in Siem Reap on 14 December 2011. The service was further adjusted to continue Phnom Penh as well, operating a triangle route, Siem Reap-Sihanoukville-Phnom Penh-Siem Reap, starting on 31 March 2013. Starting in September 2013, the airline was scheduled to provide a Siem Reap-Sihanoukville route twice daily during the high peak season.