The present study was carried out to elucidate a centrally acting muscle relaxant effect of chloroform soluble fraction and its component, namely, ligustilide, cnidilide and senkyunolide obtained from the rhizome of Cnidium officinale Makino. These three compounds were isolated from the chloroform soluble fraction by column chromatography on silica gel. The centrally acting muscle relaxant effect was investigated on the crossed extensor reflex in anesthetized rats and these samples were suspended in 0.5% carboxymethyl cellulose solution and administered i.p. These three compounds as well as the chloroform soluble fraction depressed the reflex response. The depressive potencies among them were almost the same and their potencies were also the same or somewhat weaker as that of mephenesin. As a curare-like action was not observed, a muscle relaxation induced by these phthalide compounds is considered to be due to central origin.