For lower limb amputees, good prosthetic fittings are important for wearing prostheses while ensuring gait stability, without skin breakdown. Poor prosthetic fittings tend to occur in the early stage after amputation because of significant changes in residual limb volume. We measured the extent of change in residual limb volume in three below-the-knee amputees by using computed tomography. The measurements were performed before and after inpatient rehabilitation for the first prosthesis. The measurement showed a remarkable change in residual limb volume in a highly active amputee without complications. In contrast, the change in residual limb volume was small in two less active below-the-knee amputees with serious complications, such as heart and renal failures. Generally, to maintain good prosthetic fittings, the first prostheses should be made during inpatient rehabilitation to facilitate maturation of the residual limbs. For the less active below-knee amputees, the prostheses could be made in the outpatient settings because the volume fluctuations of their residual limbs are small and the functional requirements for their daily living are modest.