Peucedanum terebinthaceum Fischer (Umbelliferae) known as "Gi Reum Na Mool" in Korea and used for the treatment of cough, phlegm, headache and common cold etc. The substances were isolated from the fruits of Peucedanum terebinthaceum and identified by UV, GLC, IR, NMR, Mass spectra and physico-chemical tests. The steroidal compounds from the fruits were identified as $eta$-sitosterol (tR 33.01 min.) and stigmasterol (tR 28.87 min.) by GLC. Substance I (colorless prismatic crystal, $C_{19}H_{20}O_5$, mp $110~111^{circ}$) was identified as decursin which is one of the pyranocoumarin. Hydrolysis of substance I with 5%-potassium hydroxide produced decursinol. Acetylation of decursinot gave its monoacetate, white needles, $C_{16}H_{16}O_5$. Substance II(light yellowish white needle crystal, $C_9H_6O_3$, mp $227~228^{circ}$) was proved to be umbelliferone. Substance I, decursin, was isolated for the first time from the fruits of Peucedanum spp. (Umbelliferae).