This paper proposes a flatness based control law for the control of the rear wheels skid of an hybrid vehicle (VELROUE). This vehicle has an ICE 1 traction and an electric propulsion, rear wheels being driven by two independent electric motors. The flatness based control law is here based on a nonlinear two state equations vehicle model, which represents most of the longitudinal dynamics. Firstly, the flat output is identified on the Bond Graph of the vehicle model, then the flat control is designed and is validated in simulation. Finally, this approach is compared to a PI controller classically used in the automotive industry.