One of coumarine compound has been isolated from the stem Polyalthya longifolia. The compound was purified by column chromatography with silica gel as absorbent. The purity of the isolated has been tested by TLC, melting point and gas chromatography.The structure of the compound was identified by means of spectroscopic include Ultraviolet Spectroscopy, Infrared Spectroscopy, 1H and 13C NMR and Mass spectroscopy . All data obtained indicate that the resulted compound is a coumarin compound with name 7-N, N-diethylamino-4- methyl coumarin.