A 66-year-old man was admitted to our intensive care unit because of severe pneumonia. He was treated with mechanical ventilation, antibiotics, and corticosteroids, but muscle weakness developed rapidly. His muscle strength declined to a Medical Research Council scale sum score of 18/60；thus, a diagnosis of intensive care unit-acquired weakness (ICU-AW) was made. The results of nerve conduction studies were compatible with critical illness polyneuropathy. Mechanical ventilation was required for 95 days because of continuous respiratory failure. Rehabilitation began at 48 hours after hospitalization and was continued to prevent immobilization even when he was mechanically ventilated. However, orthostatic hypotension developed and inhibited mobility training. Physical and occupational therapies provided muscle strengthening exercises followed by a progressive mobility program that assisted him to raise his head, sit on the edge of the bed, and stand up. The intervention was performed within safety criteria of vital signs and the rating of perceived exertion (RPE) Borg scale between 11 and 13. It resulted in the attenuation of orthostatic hypotension and the recovery of muscle strength. He finally achieved independence in activities of daily living and the ability to walk without help after 271 days of admission. This case report suggests that long-term rehabilitation within safety criteria of vital signs and RPE Borg scale between 11 and 13 is safe and feasible without overuse weakness for ICU-AW with orthostatic hypotension.