Objective To search for the gene encoding specific antigen of Ancylostoma caninum that induces host′s protective immunity. \ Methods\ A lambda ZAPⅡ cDNA library of A.canium was screened with sera from dogs \{immunized\} subcutaneously with hookworm larvae(L3). After sequencing, insert gene (AcAg) from positive clones was \{ligated\} into PUC18 and PET28C. Recombinant pET28C plasmid was induced to expressed protein in the E.coli BL21. The \{characteristic\} of recombinant protein is analyzed by SDS\|PAGE and Western bloting assay. \ Results \ Five positive \{clones\} were obtained, and proved to be the same. The insert gene (AcAg) in pET28C vector expressed a recombinant \{protein\} of about 43 kDa. Using Western bloting assay, this protein was recognized by the sera from dog immunized with \{Ancylostoma\} caninum third\|stage infected larvae and used for screening library. \ Conclusion \ The AcAg, which \{exhibits\} 35% homologous to Caenorhabditis elegans gene unc\|89, is a novel specific antigen of A.caninum. Its ability to elicit the \{protective\} immunity and the probability of the recombinant protein as a vaccine need to be further evaluated.