The Lao Airlines ATR-72 turboprop plane, carrying 49 people from the capital Vientiane, crashed eight kilometres short of its destination at Pakse airport in the southern Lao province of Champasak.
A preliminary report said the aircraft could have hit a tree before plunging into the river. Officials ruled out the possibility of survivors.
Forty-four passengers on board the flight included 17 Lao, seven French, five Australians, five Italians, five Thais, three South Koreans, two Vietnamese, and one each from the US, China, Taiwan, Canada and Malaysia.
Thai police spokesman Piya Uthayo said Thailand has offered to help Lao authorities identify the bodies.
A Lao aviation official said typhoon Nari could have been a factor in the plane crash but an official statement on the cause of the crash has yet to be released.