Mesenchymal stem cells (MSCs) form part of tumor stroma, and are typically considered to be pro-tumorigenic, promoting continuing tumor growth and metastasis. Here, we describe a mechanism by which MSCs may be anti-tumorigenic, through inhibition of breast cancer cell migration and invasion, an important part of metastasis. MDA-MB-231 and T47D cells were co-cultured in a Transwell insert above MSCs or MSC conditioned media and their migration or invasion through Matrigel measured. The conditioned media was found to inhibit breast cancer cell movement. TIMP-1 and TIMP-2, inhibitors of matrix metalloproteinases (MMPs), were identified as candidates for this inhibition and enhanced secretion of MMPs was not sufficient to counter the anti-migratory effects of TIMP expression. Inhibition of TIMP activity showed that TIMP-1 and TIMP-2 together were largely responsible for the reduction of migration and invasion by MSCs. Therefore, MSCs may play anti-tumorigenic, anti-metastatic roles in tumor development, with the overall outcome dependent upon the balance of pro-and anti-tumorigenic molecules secreted.