To establish a model of gastric precancerous lesion by using Aristolochic manshuriensis which contains aristolochic acids.The SD rats were randomly divided into four groups: control and three different doses of ethanol extractive of A. manshuriensis (EEA) (corresponding to aristolochic acid I 2.5, 5.0, 10.0 mg x kg(-1)), respectively. EEA was intragastrically given to rats every other day. At the end of the 10th, 15th, 20th week, part of the rats in each group was sacrificed and the stomachs were weighed. The gastric tumor was assessed by the weight and the relative stomach weight to the body weight. The stomachs were fixed in 4% neutral formalin, and the paraffin imbedding tissues were sliced and HE stained. Histomorphology was observed under the light microscope to determine gastric hyperplasia, mucosa precancerosis (atypical hyperplasia) and gastric cancer formation.The rats treated with different doses of EEA for 10 weeks induced mucosa papillary, epithelioma hyperplasia. Histological observation showed mucosa precancerosis lesions characterized as atypical hyperplasia at the dose levels corresponding to aristolochic acid I 5.0 and 10.0 mg x kg(-1) treated for 10 weeks. The incidence rate of gastric precancerosis in those two groups was 100% at the 15th week. Malignant tumors were observed in most of the animals in 10.0 mg x kg(-1) group. The animals in 5.0 mg x kg(-1) group were well tolerant compared to 10.0 mg x kg(-1) group during the course of experiment, so the dose of aristolochic acid I 5.0 mg x kg(-1) and 10-15 weeks treatment were considered to be optimum to establish the model of gastric precancerosis.A rat model of gastric precancerosis can be induced within a short duration by giving an oral administration of the ethanol extract of A. manshuriensis which contains aristolochic acids.