A one-step method for the purification of anti-hepatitis B core antigen monoclonal antibody from mouse ascites was established.The ascites were purified by protein A affinity chromatog. after centrifugation, filtration, etc.The exptl. parameters including sample loading pH, NaCl concentration, the type of elution, pH value and flow rate were optimized.The biol. activity of purified monoclonal antibody was detected by ELISA technol.The results showed that the optimized loading medium was 20 mmol/L phosphate buffer containing 3.0 mol/L sodium chloride at pH8.0, and the monoclonal antibody was eluted by 0.1 mol/L Gly-HCl at pH 3.0.The purity of obtained monoclonal antibody was more than 95 % and recovery reached 75%.The biol. activity of purified monoclonal antibody did not decline.This experiment showed that the protein A affinity chromatog. was a simple, rapid and effective method to purify anti-HBcAg monoclonal antibody.