For virtual evaluation of universal design products, it is necessary to synthesize natural grasps for various hands including those with disability. As one of the disabilities, we focused on the limitation of the thumb’s range of motion (ROM). For example, carpal tunnel syndrome (CTS) is a typical disease that limits thumb’s ROM. Though there is no doubt that the range of motion affects the whole grasp, detailed grasp strategy has not been studied so far due to the difficulties in collecting data from such patients. Therefore, in this paper, we propose to synthesize grasping postures by the thumb’s ROM-limited digital hands based on the observation of an actual subject whose hand is artificially-disabled. The synthesized postures of the healthy hand and the thumb’s ROM-limited hand were obviously different. We applied a contact-region-based method for grasp synthesis for ROM-limited hand and succeeded in synthesizing the grasping postures that reflect the features of the thumb’s ROM-limited hands’ grasps.