A 69-year-old man with ulcerative colitis (UC) developed sensorimotor polyneuropathy. First, he received salazosulphapyridine (SASP) as treatment for the UC. The symptoms of UC disappeared immediately, but he developed skin eruptions and dysesthesia in his lower limbs. When SASP was changed to 5-aminosalicylic acid (5-ASA), his skin eruptions were resolved, however, he developed weakness and atrophy in his right arm as well as progressive worsening of the dysesthesia in his legs and gait disturbance. Deep tendon reflexes (DTR) were absent in all extremities. After 5-ASA was discontinued, the polyneuropathy symptoms recovered gradually. This clinical course suggests that the sensorimotor polyneuropathy may have been caused by 5-ASA.