The field of bispecific antibodies is an evolving field of research that has increasing clinical appeal. The fusion of two antibodies or antibody fragments introduced a new way to override natural specificity of T cell and induce effector responses against tumor targets in MHC-unrestricted manner. Initial experiences with bispecific antibodies demonstrate both the promise for and limitations of this anti-cancer strategy. Significant body of work has shown that bispecific antibodies have potential to induce T cell mediated anti-tumor responses in pre-clinical models. However, immunotherapy with bispecific antibodies in humans has yet to prove its value in clinical settings. In addition, the production of high-quality bispecific antibodies for clinical applications, the optimal size and avidity of bispecific antibodies, and in vivo T cell pre-activation remain critical issues. In this review, we summarize recent progress in bispecific antibody-based immunotherapy and address essential aspects of this anti-cancer strategy.