Bone marrow-derived mesenchymal stem cells (MSCs) are capable of migrating and homing to brain tumors in vivo and therefore is a promising targeted-delivery vehicle in cancer gene therapy. MSCs are transfected or transducted with the therapeutic genes and achieve stable expression in vitro, then are delivered to the host to exert their therapeutic effects. The Ex Vivo gene transfer of MSCs has been studied in several types of tumors including gliomas, and results were postive. The safety of MSC-based gene delivery remains to be controversial. The interactions between MSCs and host tumor cells need to be investigated.