Abstract: Recognition proteins play an important role in the immunodefense system of invertebrates. The haemolymph of the Slipper oyster, Crassostrea iredalei, contains a heparin-binding protein with a molecular weight of 35 kDa as determined by SDS-PAGE analysis. The protein was purified using column chromatography. This binding protein possesses a serine protease activity thus it is capable of activating the prophenoloxidase-activating (proPO) system. However, the protein lacks β-1,3-glucanase activity. Using rabbit antiserum against the isolated protein in immunodiffusion and immunoblotting assays it produced a single precipitant and a single band, respectively. However, N-terminal amino acid sequence of BGBP: Threonine-Alanine-Arginine-Asparagine-Glutamic acid-Alanine-Asparagine-Valine was similar to Cavortin (AAT44352) and extracellular superoxide dismutase (AAY60161) from C. gigas.