Objective: To study the preparation and characterization of monoclonal antibody (McAb) against carcinoembryonic antigen (CEA). Methods: CEA antigen was extracted from metastasized liver of patients with colorectal cancer and used for the preparation of McAb against CEA by hybridoma technique. Immunoreactivity of McAb to CEA antigen was evaluated using ELISA. Mouse ascites was purified by two steps, high performance liquid chromatography (HPLC) using protein A and high performance hydroxylapatite (HPHT). Normal adult tissues and tumor specimen were used for immunohistochemical evaluation of the McAb. Isotope 99mTc labeled CEA McAb was used for biodistribution in tumor-bearing mouse. Results: Purified CEA antigen was a glycoprotein of 180 kD. Anti-CEA McAb affinity constant was 7.4x109/M. The McAb showed positive staining in 54-88% of colorectal cancer, gastric cancer and lung cancer, while negative for normal tissues. 24 hours after injection of 99mTc labeled McAb, tumor ID%/g was higher than 15% and tumor/blood, tumor/kidney and tumor/liver were 1.82, 1.51 and 2.92 respectively. T/NT ratios of other viscera were over 3.0. Conclusion: Purified CEA antigen had very good immunogenicity. The anti-CEA McAb was highly specific. 99mTc labeled McAb was stabled both in vivo and in vitro. In vivo distribution result was satisfactory. McAb CL58 may be useful for RII and RIGS.