Microtus fortis is a naturally vertebrate host resistant to Schistosoma japonicum infection. In order to understand the molecular mechanism and identify the molecules related to the natural resistance to S. japanicum infection of M. fortis, we screened a gene pool named gE76 by expression cloning and proved it to have high anti-schistosomula effects in our previous work. In this study we identified a clone named gE76.44. We found that the conditioned medium of pcDNA1.1-gE76.44 caused 14.0% schistosomula death rate in 96h, which was significantly higher than that of negative control (P<0.05). The gE76.44 was sequenced and the full-length cDNA was 2008bp with ORF of 1590bp encoding a polypeptide of 529 amino acid residues. Bioinformatics analysis indicated it was the homologue of karyopherin alpha 2 (KPNA2). To further confirm its anti-schistosome activity, we inserted full length of Mf-KPNA2 (KPNA2 of M. fortis) gene into a retroviral expression vector pLXSN and packaged the recombinant virus with PA317 cells. Mice infected with S. japanicum cercariae were administrated by intravenous injection through tail vein and treated with pLXSN-KPNA2. Adult worms and egg reduction were counted after heart perfusion of mice 42d after infection. We found that compared with the control, mice injected with Mf-KPNA2 had 39.42% worm burden reduction and 76.50% reduction in LEPG (liver eggs per gram) (P<0.01), indicating its anti-schistosome effect of Mf-KPNA2 in vivo. Taken together, the results suggested Mf-KPNA2 as a novel anti-schistosome molecule in vitro and in vivo.