AIM: To investigate H2O2-induced promotion proliferation and malignant transformation in WB-F344 cells and anti-tumor effects of ursolic acid(UA) and oleanolic acid(OA). METHODS: WB-F344 cells were continuously exposed to 7 x 10-7mol/L H2 O2 for 21 d. Observations of cell morphology, colony formation rates, flow cytometric analysis of cell cycle changes and aneuploidy formation indicated that H2 O2 was able to induce malignant transformation of WB-F344 cells. We treated malignantly transformed WB-F344 cells with 4 μmol/L OA or 8 μmol/L UA for 72 h and analyzed the cell cycle distribution by flow cytometry. RESULTS: MTT assay showed that 7 x 10-7mol/L H2 O2 decreased G1 phase subpopulation from 73.8% to 49.6% compared with the control group, and increased S phase subpopulation from 14.5% to 31.8%(P < 0.05 vs control group). Cell morphology showed that nucleus to cytoplasm ratio increased, many mitotic cells, prokaryotes and even tumor giant cells were shown in H2 O2-induced WB-F344 cells. Fluorescence activated cell sorting analysis showed that WB-F344 cell aneuploidy increased to 12% following H2 O2 treatment. Flow cytometric analysis of the transformed WB-F344 cells following treatment with OA(4 μmol/L) and UA(8 μmol/L) showed that OA increased G1 subpopulation to 68.6%, compared to 49.7% in unexposed cells. UA increased G1 subpopulation to 67.4% compared to 49.7% in unexposed cells(P < 0.05 vs H2 O2 model group). CONCLUSION: H2O2 causes the malignant transformation of WB-F344 cells. OA and UA exert anti-tumor effects by inhibiting the proliferation in malignantly transformed WB-F344 cells. AIM: To investigate H2O2-induced promotion proliferation and malignant transformation in WB-F344 cells and anti-tumor effects of ursolic acid (UA) and oleanolic acid (OA). METHODS: WB-F344 cells were continuously exposed to 7 x 10-7 mol / L H2 O2 for 21 d. Observations of cell morphology, colony formation rates, flow cytometric analysis of cell cycle changes and aneuploidy formation indicated that H2 O2 able to induce malignant transformation of WB- F344 cells. We treated malignantly transformed WB-F344 cells with 4 μmol / L OA or 8 μmol / L UA for 72 h and analyzed the cell cycle distribution by flow cytometry. RESULTS: MTT assay showed that 7 × 10 -7 mol / L H2 O2 decreased G1 phase subpopulation from 73.8% to 49.6 % compared with the control group, and increased S phase subpopulation from 14.5% to 31.8% (P <0.05 vs control group). Cell morphology showed that nucleus to cytoplasm ratio increased increased in many mitotic cells, prokaryotes and even tumor giant cells were shown H2 O2-induced WB-F344 ce Flu cytometry analysis of the transformed WB-F344 cells following treatment with OA (4 μmol / L) and UA (8 μmol / L) UA increased Gl subpopulation to 67.4% compared to 49.7% in unexposed cells (P <0.05 vs. H2O2 model group). CONCLUSION: H2O2 causes the malignant transformation of WB-F344 cells. OA and UA exert anti-tumor effects by inhibiting the proliferation in malignantly transformed WB-F344 cells.