Astragalus membranaceus (AM) has been widely used for treating liver diseases in traditional Chinese medicine. Experimental evidence indicates that it has antitumor potential. In this study, the effect of AM on hepatocarcinogenesis induced by diethylnitrosamine (DEN), two-thirds partial hepatectomy, and 2-acetylaminofluorene (2-AAF) (DEN-PH-AAF) was evaluated using glutathione S-transferase placenta form (GST-P) as marker. First, rats were injected intraperitoneally (i.p.) with DEN (200 mg/kg in saline), a two-thirds partial hepatectomy was carried out 2 weeks later, and the rats were then placed on a basal diet containing 0.02% AAF from week 3 to week 8 to induce hepatocarcinogenesis. The rats were given AM (90 mg/kg or 180 mg/kg body weight) by gavage from week 3 to week 8 (treatment groups). The formation of GST-P-positive foci and the expression of GST-P protein and mRNA caused by DEN-PH-AAF were reduced in the treatment groups, which clearly suggests that AM is effective in delaying DEN-PH-AAF-induced hepatocarcinogenesis.