This paper investigates a fractional terminal sliding mode control for flexible spacecraft attitude tracking in the presence of inertia uncertainties and external disturbances. The controller is based on the fractional calculus and nonsingular terminal sliding mode control technique, and it guarantees the convergence of attitude tracking error in finite time rather than in the asymptotic sense. With respect to the controller, a fractional order sliding surface is given, the corresponding control scheme is proposed based on Lyapunov stability theory to guarantee the sliding condition, and the finite time stability of the whole close loop system is also proven. Finally, numerical simulations are presented to illustrate the performance of the proposed scheme.