While use of RNA interference results in total loss of the target proteins, antibody binds to the corresponding epitope region but does not affect the expression level of the target protein. Consequently, it may offer opportunity to selectively evaluate biological function of selected domains from multi-domain proteins where each domain participates in its unique biological function. Although several methods for antibody transduction into live cells have emerged, most of them are suffered from harsh conditions or low delivery efficiency. In this study, we developed antibody transducer by conjugating IgG Fc-binding peptide (FcBP) with Tat, a cell penetrating peptide (CPP). FcBPCPP fusion peptide and FcBP-eGFP-Tat fusion protein, thus prepared, self-assembled to IgGs in situ upon their simple mixing in cell growth media, and translocated into the cytosol of live cells. Since FcBP-CPP reversibly binds to Fc-region of antibodies it neither impairs the structural and functional integrity of antibodies nor requires additional effort to modify antibodies. This represents the first synthetic peptide reagent, enabling antibody delivery into live cells in the absence of any additional detergents or other physical treatments such as electrophoresis or microinjection.