Leigh Griffiths and Gary Mackay-Steven scored in the opening quarter of the match to set up a morale-boosting win ahead of Wednesday’s Champions League qualifier against FK Qarabag at Celtic Park.
Charlie Mulgrew tested Rennes goalkeeper Benoit Costil with a free-kick after 10 minutes following a foul on Celtic skipper Scott Brown.
But the Hoops made the breakthrough two minutes later when Griffiths collected the ball on the right flank and drifted into the penalty area before squeezing the ball past three defenders and Costil.
Celtic doubled their advantage on 22 minutes when Stuart Armstrong split the Rennes defence with a wonderful pass and Mackay-Steven provided a composed finish with his left foot.
Six minutes later Hoops ‘keeper Craig Gordon was called into action to block a shot from Steven Moriera before the rebound was blasted over the bar.
The visitors were becoming frustrated, though, and Nir Bitton, Mackay-Steven and Mulgrew were all on the end of heavy challenges, with the latter forced out of the match.
Celtic made several more changes at the break and throughout the second half with manager Ronny Deila keen to avoid any injuries before the midweek European encounter.
Leonardo Fasan was one of the replacements, as he took over from Gordon between the sticks, and he produced a brilliant save (73) to keep out an Ola Toivonen header.
Anthony Stokes then attempted to curl a shot towards the far post from inside the penalty area but his effort landed on the roof of the net.
Four minutes from time Fasan produced another fine save to deny Toivonen when he got down to push away an angled drive.
Celtic had the final chance three minutes from the end when Tom Rogic was brought down as he burst towards goal, and although Stokes beat the wall with the free-kick the ball rose over the bar.