Sodium polystyrene sulfonate (SPS) (Kayexalate) is a cation-exchange resin used to treat hyperkaliema. Administered with sorbitol, it usually has minor adverse effects, but it may cause colonic or intestinal necrosis in uremic patients. We report an unusual case of rectal stenosis due to SPS crystals in a 46-year-old man. The patient had been involved in a car accident with severe thoracic and abdominal trauma. During his hospitalization, he presented traumatic acute pancreatitis with ischemic colitis because of hypotension, and acute renal insufficiency treated by hemofiltration and Kayexalate administered by nasogastric tube without sorbitol. Left colon was resected and Hartmann's procedure was performed. Restoration of the colon continuity was performed 13 months later. The rectal lumen was narrowed with a thickened rectal wall. Microscopic examination revealed fibrosis of the submucosa containing numerous basophilic polygonal crystals surrounded by macrophages. This is the first case report of rectal stenosis caused by foreign body reaction to SPS crystals after ischemic colitis.