Objective To establish the animal model bearing BRCA1-overexpressing breast tumor in athymic mouse so as to investigate the effects of lovastatin (LOV) on the growth of the xenograft tumor and understand its mechanism. Methods After amplification and identification, pcDNA3-beta-HA-hsBRCA1 plasmid was transfected into MCF-7 cells by liposome transfection to deliver a high level of BRCA1 gene expression examined with RT-PCR and Western blotting (named MCF-7 BRCA1 ). Twenty athymic mouse models of BRCA1-overexpressing xenograft tumor were established by respectively inoculating 2?10 6 MCF-7 cells and MCF-7 BRCA1 cells to right anterior part of the back. Four weeks later, lovastatin at the dose of 50 mg/kg was injected around the tumor for 10 d. Then the tumor volume was measured, the histopathological changes of xenograft tumor were observed with electron microscope by HE staining, the expressions of cyclinD1, CDK4 mRNA and protein were detected by RT-PCR and Western blotting. Results The athymic mouse model of xenograft breast tumor was successfully established after MCF-7 cells were transfected with pcDNA3-beta-HA-hsBRCA1 plasmids. The incidence rate of xenografted breast tumor in athymic mouse was 100%. Routine HE staining of paraffin-embedded section proved that the tumor was a mammary carcinoma in nature. Treated with lovastatin for 10 d, the tumor volume of mouse implanted with MCF-7 cells was large (0.48 cm 3 ) and there was a slight change in expressions of cyclinD1, CDK4 mRNA and protein, while the tumor volume of mouse inoculating MCF-7 BRCA1 cells was small (0.21 cm 3 ) and the expressions of cyclinD1, CDK4 mRNA and protein obviously descended. The two groups showed diminution in cancer cells and increase of necrosis, more significant in those mice inoculating MCF-7 BRCA1 cells. Conclusion Lovastatin could resist the proliferation of BRCA1-overexpressing breast tumor, which may relate to the decrease of the cyclinD1, CDK4 mRNA and protein expressions.