Gene therapy holds great promise for the treatment of cancer. The success of the strategy relies on effective gene transfer into tumor microenvironments. Although a variety of gene delivery vehicles, such as viral vectors, has been developed, most of them suffer from some limitations, including inadequate tumor targeting, inefficient gene transfer, and potential toxicity. This situation suggests that it is necessary to develop novel vectors for effective tumor-targeted gene transfer. The discovery of tumor-targeting bacteria has spurred interest in the use of these bacteria as gene transfer vectors. In this review, we focus on the current status of the development of bacterial vectors for cancer gene therapy and highlight some of the directions that the field may take.