Lung cancer carries one of the highest mortality rates among all cancers, often being diagnosed at advanced stages with limited treatment options compared to other malignancies. This study focuses on calnexin as a potential biomarker for diagnosis and treatment of lung cancer. Calnexin, a molecular chaperone integral to N-linked glycoprotein synthesis, has shown some associations with cancer, but no targeted therapeutic or diagnostic methods have been proposed. Through 1D-LCMSMS, we identified calnexin as a biomarker for lung cancer and substantiated its expression in human lung cancer cell membranes using Western blotting, flow cytometry, and immunocytochemistry. Anti-calnexin antibodies exhibited complement-dependent cytotoxicity against lung cancer cell lines, resulting in a notable reduction in tumor growth in a subcutaneous xenograft model. Furthermore, we verified the feasibility of labeling tumors through in vivo imaging using antibodies against calnexin. Additionally, exosomal detection of calnexin suggests the potential utility of liquid biopsy for diagnostic purposes. In conclusion, this study establishes calnexin as a promising target for antibody-based lung cancer diagnosis and therapy, unlocking novel avenues for early detection and treatment.