Recombinant Anti-Ad fiber knob x Anti-CEA Bispecific Antibody (scFv-Fc-scFv) is designed to be expressed as one chain, then assembled to a homodimer of bivalent scFv fragments and the Fc region of IgG. The anti-Ad fiber knob scFv is fused to the N-terminus of Fc via a hinge region while another anti-CEA scFv is linked to the C-terminus of Fc. This scFv-Fc-scFv format has 2+2 antigen-binding valency by employing different scFv fragments. 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.