This paper investigates the synchronization of perturbed incommensurate fractional-order chaotic systems, and proposes a modified adaptive controller for fractional-order chaos synchronization based on Lyapunov stability theory, fractional order differential inequality and adaptive strategy. This synchronization approach is simple, global and theoretically rigorous. It enables synchronization of perturbed fractional-order chaotic systems to be achieved in a systematic way. Simulation results for fractional-order Qi chaotic system are provided to illustrate the effectiveness of the proposed scheme.