The count of more than 4,500 ballots took all night.
Neither candidate campaigned in the U.S. island territory in person, but both did long-distance media interviews and bought campaign ads.
The count, completed this morning, showed that Obama's slate received 2,264 votes to Clinton's 2,257.
That means the candidates will split the four pledged-delegate votes. (Eight pledged delegates will attend the Democratic National Convention in August, each with half a vote.)
The territory also will send five superdelegates to the Denver convention.
All-day voting Saturday had people lining up at 21 caucus sites around Guam, which has unexpected importance in this Democratic race, in which every delegate matters.
There was no direct presidential vote, but each candidate had a slate of supporters on the ballot.
U.S. citizens on the island, however, cannot vote in the November general election.