This paper is concerned with an adaptive control of free-flying space robots with uncertain inertial parameters of payloads. It is applicable to control all of the position and attitude of the satellite vehicle as well as that of the manipulator hand if the satellite has position/attitude control devices, e.g., thrusters and control momentum gyros. The proposed adaptive control realizes high control performance by estimating unknown parameters even if a control model has an error to the real plant caused by the payload. Asymptotic stability of the adaptive control is proven by Lyapunov's second method. The effectiveness is examined by numerical simulations for a hardware experimental system.