Objective To construct a new recombinant immunotoxin expression vector fused with a murine interleukin18(IL18) gene and a truncated pseudomonas exotoxin (PE38) gene, and examine the expression of IL-18-PE38 fusion protein in Escherichia coli (E. coli). Method Murine IL-18 (mIL-18) cDNA was cloned from murine liver tissue through reverse transcription-polymerase chain reaction (RT-PCR). The mIL-18 cDNA was ligased with a PE38 gene carried by PRKL expression vector through T4 DNA ligase and constructed into fusion protein expression plasmid PRKL-IL18-PE38. The recombinant vector was identified by restriction endonucleases digestion, PCR and DNA sequencing. After transformed into E.coli BL21 and induced by IPTG, the expressed product was obtained and the molecular weight and specificity were determined by SDS-PAGE and Western-blotting. Result The new recombinant immunotoxin expression vector was constructed successfully. DNA sequencing revealed that the mIL-18 and PE38 gene were consistent with NCBI Gene Bank. The IL-18-PE38 fusion protein was expressed in E.coli BL21, and Western-blotting analysis indicated that the molecular weight of the expression product is about 56 kDa, and could react with the specific antibody against mIL-18. Conclusion IL-18-PE38 recombinant immunotoxin expression vector will provide the basis for study on the targeted cytotoxic activity to Th1 cells and may have some potential value in the treatment of Th1 cell-mediated autoimmune diseases.