Rovers set the pace from the start and impressive teenage defender David Wheater was unlucky to see a tremendous header blocked on the line by Sean Clohessy following a third minute corner.
Gillingham threatened in the first half and their best effort came in the sixth minute when Clohessy's cross was palmed down by Alan Blayney and Gary Mulligan followed up to have a shot that was saved by the keeper's legs.
Doncaster resumed control and on-loan striker Ross McCormack hit the crossbar with a cracking 20-yarder in the 15th minute and Jason Price's follow-up shot deflected just past the post.
A Tommy Black free-kick was headed out by Graeme Lee straight to the feet of Mulligan in the 25th minute but his volley was way off the mark.
Doncaster made the breakthrough a couple of minutes later when Kevin Horlock played the ball into the middle and Wheater forced the ball home from close range following a goalmouth scramble.
Price sent a diving header just wide four minutes later as Rovers continued to call the tune following good work by Dave Mulligan and Paul Green.
Rovers had the points wrapped up by the interval when McCormack sent Jason Brown the wrong way from the penalty spot after Leon Johnson had committed a clumsy foul on Price.
The suprise was that Doncaster did not go on to score more with the visitors looking decidely to second best.
Gillingham battled in the second half but their efforts to try and get back into the game were feeble and Doncaster went on to win with ease.
Dave Mulligan had a free-kick comfortably saved and substitute Michael McIndoe went close with a 20-yard volley which was saved at the second attempt as Rovers threatened to run riot.