Analysis of the root extract of Peucedanum formosanum (Taiwan Qian-Hu) led to the isolation of 32 known compounds. The structures of these isolates were determined by spectral data. Some of them displayed strong anti-platelet aggregation activities. Analysis showed that most of the constituents found in P. formosanum were the same as those found in P. praeruptorum (Bai-Hua Qian-Hu), in that many isolates of both plants’ roots belong to seselin-type dihydropyranocoumarins and psoralen-type furanocoumarins.