Objectives: In this study, we used female rats, which were treated with 7,12-dimethylbenz(a)anthracene (DMBA) to induce breast tumors and with the concomitant of alcohol intake.The role of alcohol in the process of breast cancer development was investigated.Materials and Methods: Forty-four SD female rats were randomly divided into 4 groups: (Ⅰ) control group;(Ⅱ) control group treated with excessive alcohol (alcohol group);(Ⅲ) mammary tumour group;and (Ⅳ) mammary tumour group treated with excessive alcohol to investigate the effects of alcohol on the biomarkers in the blood, liver and tumour tissues of the rats with mammary tumours.We analyzed the liver function tests, vascular endothelial growth factor (VEGF) and matrix metalloproteinase-2 (MMP2), reduced glutathione (GSH), Bax and Bcl-2 and pi calss of glutathione S-transferase (GSTP) in the studied rats.Results and Discussion: The VEGF and GSH levels were lower in the groups with alcohol intake than those in the DMBA group, which indicates the ability of DMBA to induce breast tumors was suppressed by alcohol intake.The expression of GSTP in their liver tissues was decreased in the rats with breast tumors, which indicates the metabolic process of DMBA could be restrained by alcohol intake.Conclusion: Alcohol consumption might inhibit the ability of DMBA to induce breast tumors;however, it will worsen the course of tumor progression after DMBA successfully induces breast tumors.