A modified sliding mode fault tolerant controller is developed for flexible spacecraft attitude stabilization control with consideration of loss of actuator effectiveness fault and actuator stuck fault. In contrast to the traditional sliding mode control, the proposed control law can avoid the chattering effect that may affect the resolution of attitude control. System uncertainties are estimated on-line by using an adaptive technique to guarantee that the proposed controller possess great robustness against external disturbances as well as uncertain and even time-varying inertia parameters. Moreover, the engineering application of the developed control law does not require any on-line or off-line knowledge of the actuator faults or the support of ground stations. The Lyapunov stability analysis shows that the resulting closed-loop attitude system is globally, uniformly and ultimately bounded with high attitude accuracy, and that the possible actuator faults are successfully compensated. Numerical simulation results of an application to a flexible spacecraft are also presented to verify the effectiveness of the control law thus derived.