Knee rotationplasty is a surgery wherein the rotated ankle serves as the new knee joint after resecting the original knee joint and lesion. However, details of postoperative rehabilitation treatment in a convalescent rehabilitation ward are not well-known. Therefore, we reported the rehabilitation progress of a 36-year-old man who underwent knee rotationplasty in the convalescent rehabilitation ward. In the early postoperative period, the surgery required no weight bearing on the operated lower limb until bone healing. Even during this period, we conducted physical therapies such as joint range of motion training and muscle strength training as outpatient rehabilitation therapy. After being admitted to the convalescent rehabilitation ward, physical therapy was intensified and the patient's rotationplasty prosthesis was then fabricated and fitted by a prosthetist and orthotist. The patient was discharged 80 days after his hospitalization and could eventually walk stably with his prosthesis and returned to work. In Japan, the length of stay in a convalescent rehabilitation ward is limited. If patients are provided with enough physical therapy during the postoperative course and rotationplasty prosthesis by a skilled prosthetist and orthotist, rehabilitation treatment after knee rotationplasty can achieve good results in a convalescent rehabilitation ward.