Introduction: Determination of treatment methods that can prevent breast cancer progression is important. The objective of the present study was to investigate the effects of endurance training on Lactate Dehydrogenase (LDH) isoenzymes expression in tumor of balb/c mice bearing breast cancer. Material and methods: In this experimental study, twenty five female balb/c mice were randomly divided in two groups including control [n=12] and trained [n=13]. Breast cancer was induced by subcutaneously injection of MC4L2 cells in mammary pad region of each mouse and trained group performed seven weeks of endurance training. Tumor lactate concentration was measured by RDI (Radioimmunoassay), LDH-A and LDH-B expression in solid tumor were measured by western blotting and LDH isoenzymes expression were separated and measured in Agarose gel. The difference of variables between groups was determined by t-student test. Results: After seven weeks of endurance training tumor lactate concentration was significantly decreased in trained group in comparison to control animals (p < 0.05). This change was associated with significant decrease in tumor expression of LDH-A (p < 0.05) and concurrent increase in LDH-B(p>0.05) in trained group. At the end of the experiment, there was more expression of LDH1 and LDH2 in solid tumors of trained group whereas solid tumors of control group had more expression of LDH4 and LDH5. Conclusion: By alleviation of tumor lactate metabolism, endurance training can be a useful method in prevention or treatment of breast cancer.