Abstract: Adriamycin (ADM), an anthracycline cytotoxic agent ,wasconjugatedwith monoclonal antibody 3H11 against gastric cancer via the dextran bridge method.The conjugate 3H11- DEX- ADM, with.molar ratio of 3H11 to ADM being 1:73, re-tained antibody activity to 86%. In the cytotoxicity assay, 3H11-DEX-ADM wasshown to exhibit increased cytotoxicity against the target cell line BGC 823. Its IC₅₀ was 3.75 fold less than that of free ADM. The antitumor effect of the conjugate was evaluated in tumor-bearing nude mice.The results indicate that the specific antibody conjugate .3H11-DEX-ADM cansignificantly inhibit the tumor growth. At the dosage level used in the presentstudy (5μg/mouse ×6 ), 3H11-DEX-ADM showed an inhibition rate of 51.5% ,whereas only moderate inhibition rates were observed with free ADM and the control cornjugate NIgG - DEX- ADM. In addition, experiment was performed to evaluate the combined cytotoxicity of3H11 - DEX- ADM and the conjugate of mitomycin C(3H11 - HSA - MMC) at dif-ferent ratios. It was shown that the combination has no synergistic effect when theirIC₅₀ was compared with that of the two conjugates used alone. The same result was ob-served on combinations of the two corresponding free drugs.