The western state, one of three voting on the measure, voted by 52.7 percent in favor to 47.3 percent against, according to the Denver Post, with over 50 percent of votes counted. CNN gave 53 percent for with 47 percent against.
A number of US states have legalized the use of marijuana for medicinal purposes, but Colorado, Oregon and Washington state all voted Tuesday on legalizing recreational use as well.
In Washington state 55 percent of voters backed the move, with 45 percent against, according to CNN and NBC, citing figures with 50 percent of votes counted.
In Oregon voters appeared set to reject the proposal, with 55 percent against and 45 percent in favor, according to CNN, with 47 percent of votes counted.