A 60-year-old woman suffered from constipation for nearly 12 years. The defecatory frequency was 1 in 7-8 days. She had been taking laxatives for 5 years. Based on the medical history and colonic transit-time test using radiopaque markers, she was diagnosed with slow-transit constipation. To exclude pelvic outlet disorders and megacolon, barium defecography and rectal balloon expulsion tests were done. A partial colectomy (sigmoid colon and partial descending colon) was performed and she was discharged routinely. Under optical microscope, fibers of the myenteric plexuses showed vacuolated degeneration between the muscularis propria layer. Under electron-microscopic examination, myelinated fibers of the pelvic parasympathetic colonic nerve showed obvious vacuolated degeneration. These findings suggest that neuropathy is likely to underline the occurrence of slow-transit constipation, in which nerve dysfunction may occur via degenerative process.