Mesenchymal stem or stromal cells (MSCs) from bone marrow or local tissues are recruited to stroma of almost all types of cancers during initiation and/or progression of cancer. The recruited MSCs and their derivative cancer-associated fibroblasts interact with cancer cells to promote stemness, invasion and metastasis of cancer cells. Targeting these cancer-recruited MSCs and/or the interaction between MSCs and cancer cells are promising strategies to improve cancer therapy. On the other hand, the unique tumor-homing capacity of MSCs makes them a promising vehicle to deliver various anti-cancer agents. This review summarized the recent advancement of our understanding on the interaction between MSCs and cancer cells, as well as the potential of MSCs for cancer therapy.