With 65 percent of precincts reporting, Romney had 41 percent of the vote, U.S. Rep. Ron Paul of Texas 25 percent, former U.S. Sen. Rick Santorum of Pennsylvania 23 percent and former U.S. House Speaker Newt Gingrich 8 percent.
It was Romney's second Super Tuesday victory, projections by CNN and other TV networks indicated. Earlier, he was projected the winner of the Virginia primary.
Romney remains well liked in Vermont -- he won the state's primary handily in 2008 -- and his opponents didn't campaign hard in the state.
Vermont has 17 delegates to the Republican National Convention in August.
Three super delegates are bound by the primary results and awarded on a winner-take-all basis.
The remaining 14 are awarded winner-take-all to the candidate who wins at least 50 percent of the vote statewide, or allocated proportionately among candidates winning at least 20 percent of the vote statewide if no one gets a majority.