Carradine was found hanged in his luxury hotel suite Thursday, the Thai newspaper the Nation reported on its website, citing unidentified police sources.
His body was found by a hotel maid Thursday morning.
A Thai police officer who is investigating the actor's death told the Associated Press that Carradine's naked body was found hanging in the closet of his suite.
The Thai newspaper reported that a preliminary police investigation found that Carradine had hanged himself with a curtain cord and that there was no sign of foul play.
An autopsy is expected to be performed today.
Chuck Binder, who was Carradine's manager, cautioned against prematurely concluding the actor committed suicide and emphasized the death was being investigated by police.
"I know David pretty well," Binder said. "I do not believe he is a candidate for suicide. He had a family. He had a life. He was happy. This movie in Bangkok was going great. He was starting three more films. He was in great spirits."
In a statement to The Times, Martin Scorsese, who had known Carradine since directing him in the 1972 movie "Boxcar Bertha," said he was "deeply saddened" by the actor's death.
"David was a great collaborator, a uniquely talented actor, and a wonderful spirit," he said.
The son of noted character actor John Carradine, David Carradine appeared in more than 100 films, including Ingmar Bergman's "The Serpent's Egg" (1977).
He also played folk singer Woody Guthrie in Hal Ashby's "Bound for Glory" (1976) and appeared with his brothers Keith and Robert in the 1980 western "The Long Riders."
More recently, he played the title character of a samurai-trained assassin in Quentin Tarantino's two-film "Kill Bill" saga (2003 and 2004).
Carradine, however, remained best known for “Kung Fu,” which ran on ABC from 1972 to 1975.
The hourlong series featured Carradine as the shaven-headed Kwai Chang Caine, the orphaned son of an American man and a Chinese woman who had been trained in a Shaolin monastery, where his blind mentor, Master Po, called his young student "Grasshopper."
When Po is murdered by the Chinese emperor's nephew, Caine kills the nephew. To avoid execution, he flees to the American West.
The series, for which Carradine received an Emmy nomination, is credited with helping popularize martial arts in the West.
But in his memoir "Spirit of Shaolin," Carradine admitted that while making the series "I was a fake."