We have recently developed the so-called recombinant immunoporter as a non-viral vector based on a single-chain antibody (scFv) derived from a monoclonal antibody B4G7 against epidermal growth factor (EGF) receptor. This immunoporter (mBBD20) was composed of single-chain antibody and negatively charged oligopeptide tail [5 units of Asn4Ser (D20)], and was expressed in yeast as a secreted protein. The purified mBBD20 was converted to an immunogene by mixing it with DNA and a cationic polymer, polyethyleneimine (PEI). The resulting complex, namely recombinant immunogene, exhibited gene transfer activity with EGFR-specificity in vitro (Suzuki et al., Gene Ther. 2003). In this paper, we further improved various conditions necessary for the formation of the proper recombinant immunogene, retaining receptor specificity of its binding, intracellular processing of the receptor-bound gene, and efficient gene expression. Moreover, we provided evidence that the recombinant immunoporter made with humanized scFv could be used as a potent gene transfer vehicle to target particular tumor cells. This approach seems worthy of clinical trial.