Eight compounds were isolated from the aerial parts of Siegesbeckia orientalis L. and their structures were elucidated by spectroscopic methods(IR, EI-MS, 13C-NMR, 1H-NMR, 1H-1H COSY, 1H-1H NOESY and 1H-13C COSY). Compounds I and II are new natural products and named siegesesteric acid(I) and siegesetheric acid(II), their structures were confirmed as ent-17-acetoxy-18-isobutyryloxy-16(alpha)-kauran-19-oic acid(I) and ent-17-ethoxy-16(alpha)-(-)-kauran-19-oic acid(II). The others were identified as known compounds: ent-16 beta, 17-dihydroxy-kauran-19-oic acid (III), kirenol(IV), beta-sitosteryl glucoside(V), heneicosanol(VI), methyl arachidate(VII) and beta-sitosterol(VIII). These compounds, except kirenol and beta-sitosterol, were isolated for the first time from the title plant.