Five kinds of furo- and pyrano-coumarins isolated from Chinese Drug “Qian-Hu”, the root of PEUCEDANUM DECURSIVUM Maxim. (= ANGELICA DECURSIVA Fr. et Sav.) and P. PRAERUPTORUM Dunn., and two kinds of furocoumarins isolated from ANGELICA EDULIS Miyabe were tested on their effects on human platelet aggregation induced by 2 μM ADP. Nodakenin ( 1) and nodakenetin ( 2) were found to show the most inhibitory activity against both primary and secondary wave of aggregation induced by 2 μM ADP. Ae-II (= vaginidin) ( 3) and Ae-III (= isopeucenidin) ( 4) showed inhibition against only secondary wave aggregation. Pd-C-V ( 6) and Pd-Ia ( 7) were rather promotive in the primary wave aggregation. Pd-C-II ( 5) and dicoumarol ( 8) showed no activity. Coumarin ( 9) and umbelliferone ( 10), a biosynthetic intermediate of Qian-Hu coumarins, showed also strong activity on primary and secondary platelet aggregation.