Abstract: The LD₅₀ of crystal-8, isolated from the root or stem of Zanthoxylum nitidum (Roxb.) DC. was 68.0±8.4mg/kg(i. p.) in mice. The contraction of the ileac muscles of the guinea-pig, induced by acetylcholine, pilocarpine, neostigmine, barium chloride or histamine, was relaxed by Crystal-8 at the concentration of 1×10^-6～1×10^-4g/ml. In mice the writhing induced by 0.1% acetic acid (0.1ml/10g) was antagonized by Crystal-8 (10 mg/kg, i. p). In rabbit the pain threshold, measured by the potassium ionophoresis method, was markedly elevated by intraperitoneal administration of Crystal-8 at the dose of 8 or 16 mg/kg. Marked elevation of pain threshold was also obtained 15 minutes after the administration of 10～20 mg/kg(i.p.)or 200 μg/kg(intraventricular inj.) as measured by the rat tail-flick method. The analgesic effect of Crystal-8 was not antagonized by nalorphine(5mg/kg, i. p.) but antagonized by reserpine (4mg/kg, i.p.).These results indicate that: the antispasmodic effect of Crystal-8 probably was produced by direct action on the smooth muscles; the analgesic effect of Crystal-8 appears to be of a central nature, unrelated to the morphine receptors, but related, to the monoamine transmitters in the brain.