The analgesic activity of an extract of the leaves of Cassia alata and kaempferol 3-O-sophoroside were studied after intraperitoneal injection in mice and rats using the tail clip, tail flick, tail immersion and acetic acid-induced writhing methods and the results compared with morphine. Maximum analgesic activity of the extract was apparent 120 min after injection. Fifty milligrams of kaempferol 3-O-sophoroside appeared equivalent to 100 mg of the extract.