The pot-loving Cheech & Chong star explained that he first noticed symptoms several years ago but was only diagnosed recently.
Chong announced his condition during an interview with CNN's Don Lemon about his support for decriminalising marijuana.
"I've got prostate cancer, and I'm treating it with hemp oil, with cannabis," he said. "So [legalising marijuana] means a lot more to me than just being able to smoke a joint without being arrested."
Chong also explained that he only began experiencing prostate problems during a three-year drug-free period.
"So I know it had nothing to do with cannabis," he said. "Cannabis is a cure."
The 74-year-old added that he doesn't actually smoke marijuana, but rather ingests the hemp oil "at night, so I won't be woozy all day".
"I'm taking it as a medicine," he said.
Chong and his comedy partner Cheech Marin continue to tour, with further shows scheduled across the US later this year.