Recombinant Anti-CEA x Anti-DTPA 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-CEA scFv is fused to the N-terminus of Fc via a hinge region while another anti-DTPA 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 be used in pretargeting system of PET, radioimaging or radiotherapy. It can mediate targeting of radioactivity to tumor cells. It is designed for the research of Breast cancer; Ovary cancer; Colon cancer; Lung cancer imaging and therapy.