Abstract: Hematoporphyrin derivative (HPD)is a photosensitizer for use in photodynamic therapy (PDT).In this paper, HPD was conjugated with monoclonal antibodies 3G9 or 3Hll for use against gastric cancer in order to enhance the photosensitive effect and reduce side effect of PDT.The biological activities of the McAb conjugates were demonstrated.The killing effect on BGC823 cells of 3G9-HPD or 3H11-HPD conjugates plus exposure to light showed 17 fold and 8.6 fold greater cytotoxicity,respectively than free HPD at an equivalent HPD concentration in vitro. When 3G9-HPD and 3Hll-HPD were used in combination at 7 : 3, 5 : 5 and 3 : 7 proportion,the cytotoxicity was increased 12.9, 11.8 and 9.4 fold on target cells, respectively. The resuls indicate that the eytotoxicity was not further enhanced by the combination scheme. When tumor-bearing nude mice were treated with the different conjugatcs. Significant inhibition of tumor growth was observed and the survival period of animals was markedly prolonged in comparison with PBS,free HPD and NIgG-HPD treated groups.