A first half Fofana goal was enough to separate the teams.
Mohammad Fofana scored the only goal of the match as Reims edge away from the relegation zone.
The forward’s 22nd minute strike saw off Rennes as the visiting side stay in ninth position.
The hosts had lost half of their last six games going into this tie so three points was the perfect result for the side.
Rennes have now failed to win for five straight Ligue 1 games.
Watch highlights from the game below