66-year-old man was hospitalized because of severe abdominal pain. He had been treated for chronic renal failure. Sodium polystyrene sulfonate (SPS) and the spherical carbon adsorbent AST-120 were routinely administered to him. However, after several treatments, his pain did not resolve and his serum creatine kinase concentration was markedly elevated, so he was transferred to our hospital. Before admission to the previous hospital, muscular weakness was noted in his extremities and those symptoms persisted. His serum potassium concentration was 1.6 mEq/L, and he was administered potassium. A lower gastrointestinal endoscopy revealed normal mucosa and SPS powder-like brownish-yellow stool containing AST-120 granules in the colorectum. After massive stool discharge, the patient's pain improved and his serum potassium concentration gradually increased. The patient was diagnosed with hypokalemic myopathy thought to be mainly caused by accumulation of SPS in the colorectum.