The defensive midfielder did not start once for the Rojiblancos in La Liga after an £8 million move to the Spanish capital in the summer, so has returned to Les Verts
He signed a five-year contract with the Rojiblancos on September 2 last year, for an estimated £8 million, but has not started a single game under Diego Simeone.
Guilavogui, who has picked up five caps for France, has made the return to Ligue 1 football on a temporary basis in a bid to boost his chances of being picked for the World Cup squad in the summer.
"I'm really happy to be back at Saint-Etienne," he told reporters. "The club have made a huge effort to bring me back. This is where I flourished."
The 23-year-old spent eight seasons with saint-Etienne before joining the Rojiblancos and has been drafted in to help the club's charge for a Champions League spot.
Les Verts currently sit fourth - two points above Olympique de Marseille and four points adrift of Lille.