With 98 percent of precincts reporting, Sanders took 59 percent of votes compared to Hillary Clinton's 40 percent.
Huge crowds of Democrats turned out for the caucus vote. Voters at East High School in Denver, in Fort Collins and in other locations had to gather outside because of the fire codes.
Sanders also won in Minnesota, Vermont and Oklahoma.
The results do not guarantee Sanders will formally take Colorado's 66 delegates. Denver7's partners at the Denver Post report that those will be selected at meetings up through the party's April 15 state convention. The state has an additional 12 superdelegates who decide their support independently, with most already backing Clinton.
The final settling of most delegates will occur based on congressional district-based math that determines 43 of the delegates, according to the Post.
Colorado is one of 12 states that voted on Super Tuesday. However, while Colorado Democrats took a presidential preference poll, Colorado Republicans did not, so there are not results on the Republican side from Colorado. Republicans decided to cancel the straw poll last year because it would force delegates to go with the caucus winner.
Colorado switched from a primary to a caucus system in 2002 and, since then, there have been several attempts to switch back. So far, none of them have been successful.
Who won the other states on Super Tuesday? ABC News is calling the following races: