Objective: To observe the targeting therapy of the hdsFv-RC-RNase recombinant single chain immunotoxin on the xenograft of the human hepatocellular carcinoma in nude mice and to explore its clinical potentiality. Methods: The prokaryotic expression vector TIG-hdsFv-RC-RNase was transformed into E.coli BL21(DE3)plys to largely express recombinant single chain immunotoxin hdsFv-RC-RNase against hepatocellular carcinoma induced by IPTG. The expressed product was purified via Ni-NTA affinity chromatography under native conditions and mildly refolded. The ELISA was used to analyze its immunological activity of antigen-binding capability. The xenogrft model of the human hepatocellular carcinoma in nude mice was established and the targeting therapy of hdsFv-RC-RNase was evaluated. Results:After induced by IPTG, a new protein band with M_r 41 000 was found in the supernatant of the bacteria and expressed in a soluble form. The expressed product was purified to homogeneity via Ni-NTA affinity chromatography under native conditions. The results of ELISA showed the refolded hdsFv-RC-RNase had the specific antigen-binding capability to the human hepatocellular carcinoma cell, but not to the normal hepatocyte (P