Provided are bispecific antibodies comprised of a single-chain unit having specificity to an immune cell and a monovalent unit having specificity to a tumor cell or a microorganism. The single-chain unit includes a single-chain variable fragment (scFv) fused to an Fc fragment and the monovalent unit includes a light chain and heavy chain pair. Also provided are methods of preparing bispecific antibodies and pharmaceutical and diagnostic uses of these antibodies.