Abstract: Objective To prepare photoimmunoconjugate of hematoporphyrin(HP) and herceptin,and study its killing and apoptosis-inducing effect on tumor cells BT-474.Methods HP-herceptin photoimmunoconjugate was synthesized with EDCI as the condensator.After exposure of the cells to 630 nm laser,the killing effect of the conjugate and cell apoptosis were evaluated by MTT assay and flow cytometry.Results Compared with free HP at equivalent dose,the immune reactivity,killing effect and the apoptosis-inducing effect of HP-herceptin immunoconjugate on BT-474 cells was enhanced(P<0.05).Conclusion The killing effect of HP-herceptin immunoconjugate is stronger than free HP on BT-474 cells.