The contents of flavonoids including quercetin, luteolin and apigenin in five species of Sonchus L.were analyzed by HPLC. The results showed that the contents of quercetin, luteolin and apigenin in S. arvensis L., S. oleraceus L.and S. brachyotus DC. were 0.101,0.185 and 0.063 mg·g^-1,0.036,0.201 and 0.069 mg·g^-1,0.052,0.113 and 0.037 mg·g^-1,respectively. In S. asper(L.) Hill, the contents of luteolin and apigenin were 0.031 and 0.018 mg·g^-1, respectively,and quercetin was not be detected. In S. lingianus Shih., the content of luteolin was only 0.084 mg·g^-1,and the contents of quercetin and apigenin were trace.The total content of flavonoids in these five species was 0.049-0.349 mg·g^-1,in which that in S. arvensis and S. oleraceus were the highest with 0.349 and 0.306 mg·g^-1, and that in S. asper was the lowest.