Abstract: The study was aimed at prokaryotic expressing cytolethal distending toxin of Haemophilus parasuis, and acted on Pig iliac endothelial cells (PIEC) to investigate toxin effects. According to the complete genome sequence of Haemophilus parasuis SH0165 (serovar 5), which finished by our laboratory, we designed a set of specific primer, the cdtA, cdtB and cdtC gene was amplified by PCR, respectively. The 681, 834 and 531 bp amplified DNA fragment was cloned into pET28a and the expression were induced in E. coli BL21 (DE3) by IPTG for 3 hours. Results of Sodium docecyl sulfatepolyacrylamide gel electrophoresis (SDSPAGE) and Western blot assay showed that the cdtA, cdtB and cdtC gene was expressed in the form of inclusion body, and the recombinant protein was about 36, 34 and 28 kDa. Recombinant toxin acted on PIEC for 3 hours in vitro, and observed the morphological change after another culture of 72 hours. These results showed that CdtABC holotoxin induced PIEC distension, vacuolization and apoptosis, while the other test groups changed unobviously. The study indicated that CDT may play an important role in the infection and pathopoiesis of bacterial.