This paper deals with the applicability of Robust Adaptive Control to the attitude motion control of large spacecraft. Large spacecraft and space structures, such as large communication satellites and the ISS (International Space Station), have been constructed on orbit. However dynamic characteristics of these structures can not be fully verified on the ground because of their size, mass and flexibility. Therefore, some unmodelled dynamics, for example, truncated vibration modes, and/or unknown elements should be taken into account for the precise and stable control of attitude motion. Based on the above consideration the applicability of the Robust Adaptive Control was carefully examined and the results of numerical simulations are given. These showed good performance of the attitude control system. We also refer to the basic idea about the modal truncation. Key words--Adaptive Control, Flexible Structure, Robust Control, Satellite