Specific primers were used to amplify the gene cfi encoding CAMP factor of Streptococcus iniae (S. iniae) DGX07. CAMP factor of natural form of S. iniae could be detected by Western-blot with anti-recombinant CAMP factor antiserum. Western-blot suggested that the amount of CAMP factor expressed in S. iniae were very low and that might be not virulent enough to trigger immune response in rabbits. Western-blot also demonstrated its non-specific binding ability to rabbit immunoglobulin G.CAMP factor showed binding and invasion ability to Epithelioma papulosum cyprini cells in vitro. However, hemolysis showed the recombinant CAMP factor could exhibit the classic co-hemolytic activity on some mammals’red blood cells but failed to cytolyse fish red blood cells, suggesting that CAMP factor lost its co-hemolysis to fish in S.iniae.