Since this protein is released into the host fluid in a fairly large amount, it could be a good candidate for immunodiagnosis of fasciolosis by F. gigantica, especially the early phase of infection. In the present study, the monoclonal antibodies (MoAbs) against recombinant F. gigantica cathepsin B3 (rFgCatB3) were produced and characterized for their binding with both the recombinant and native CatB3 in various parasite’s tissues at various stages of the life cycle.