Objective: MSCs are multipotent adult stem cells with the ability to home in on sites of injury. They can be used as a potential vehicle for gene and cell therapy. Lack of immunogenicity and immunosuppressive phenotypes lead to expanded investigation of their homing in on tumors. Materials and Methods: Balb/c mice were implanted with adenocarcinoma of breast, making a model of breast cancer. GFP (green fluorescent protein ) expressing mesenchymal stem cells were cultured and injected to the tail vein of all breast cancer balb/c mice models.Three mice were sacrificed after 4, 12 and 15 days each. Samples of liver, lung, spleen and bone marrow were assayed by flowcytometry, comparing with the control group. Results: Flowcytometry analysis showed that the concentration of MSC in lung tissue was higher than the other tissues. Minute amount of cells were seen in spleen and bone marrow tissues. Conclusion: Increased tendency of MSCs to the lung tissue may have stemmed from entrapment of these cells in this tissue.Increasing MSC number may compensate the lung entrapment. Moreover using more sensitive methods may help to detect probable implanted cells.