Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (Diabody-Fc) is a fusion protein of two diabodies connected together by an Fc region. In a diabody, the two scFvs with short linkers are from anti-Ad fiber knob and anti-CEA antibodies. The VH and VL domains form an inter-chain pairing. The diabody with different specificities is fused to the Fc fragment, which results in 2+2 antigen-binding valency and exerts Fc-mediated functions or just extends the half-life. This BsAb can retarget of adenoviral vectors to tumour cells. It can be used in cancer gene therapy to transfer a therapeutic gene into tumour cells aiming at selective and efficient cell killing.