It was carried out to detect the analgesic action of piperine by hot-plate method and to elucidate its mechanism in rats. Piperine (30mg/kg i.p.) produced profound analgesia, which was blocked by naloxone (10mg/kg). Chronic intraperitoneal administration of piperine significantly increased the contents of $eta$-endorphin in rat midbrain. In the chronic piperine-treated groups, significant decreases of maximum opiate binding were observed. However, Kd value in these groups were not changed.