Slovenian Grega Bole of Lampre was second and Dutchman Lieuwe Westra of the Vacansoleil team finished third.
Bradley Wiggins retained the overall leader's yellow jersey, remaining six seconds clear of American Levi Leipheimer.
The Briton looked comfortable in matching stage three winner Alejandro Valverde up the final climb into Rodez, ensuring that there was no challenge to his position in the general classification.
And the 183km of racing culminated in a sprint finish, with Meersman emerging a surprise victor.
"I was third yesterday, and today the team worked all day," the Belgian said. "That gave me confidence and I'm really glad there was a victory.
"Today I was fast but I'm just happy I could win and I'm happy with the victory.
"We had a little roundabout with roughly 200 meters to go and I was in fifth position. I thought I was too far back and I was waiting and waiting and then I sprinted."
Jean-Christophe Peraud (Ag2r-La Mondiale), Pierrick Fedrigo (FDJ-BigMat) made the early move just minutes into the stage, and were allowed to escape by the peloton, while Leigh Howard (GreenEdge), Luis Angel Mate (Cofidis) and Bart De Clerq (Lotto Belisol) caught up to form a five-man breakaway.
Having built up a five minute and 20 second advantage, they were allowed to remain out in front without the bunch giving great chase, but the gap dwindled until it was only 90 seconds with 40km remaining.
As the breakaway riders were caught, Andreas Kloden made a move of his own, but with the German having failed to gain sufficient advantage on the climb, the sprint became inevitable.
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