Microtus fortis (Mf) is resistant to Schistosoma japonicum (Sj) infection. To explore if Mf responses to special Sj antigens after infection, Sj adult worm cDNA library was screened with sera from infected Mf. Twelve positive clones were obtained after rescreening. After automatically excised with the helper phage, positive clones were further identified by PCR. The size of Sj cDNA fragments in positive clones ranged from 300 bp to 1.8 kb. Six of these fragments were 300 bp, one was 1 kb, and five were 1.8 kb in size. The results indicate that the infected Mf serum could recognize Sj specific antigens. It is valuable to further study the immune protection of these cloned molecules.