To evaluate the inhibition effect of immunoconjugate of doxorubicin(DXR) with a monoclonal antibody, 5F11 on human lung cancer cells and its reversal effect on resistant lung cancer cells to chemotherapeutic drug.DXR was attached to 5F11 using dilute glutaraldehyde crossing.The antitumor activity of immunoconjugate, 5F11-DXR, against the sensitive antigen-positive cell line, A2, drug-resistant antigen-positive cell lines, 801-D and 801-DDXR, and antigen-negative cell line, ascite cancer cell was evaluated by human tumor cell cloning assay and dye exclusion assay.According to the results of various assays, comparing with single DXR, 5F11-DXR could significantly increase the cytotoxicity to A2, 801-D and 801-DDXR cell lines with a DXR concentration of 0.4 μg/ml(P0.05).5F11-DXR can remarkably increase the cytotoxicity of DXR to the sensitive target cells and even effectively reverse the drug-resistant cell lines to DXR. There is no significant difference between 5F11-DXR and DXR in killing antigen-negative cancer cells.