Malignant mesothelioma (MM) is a fatal tumor caused by past exposure to asbestos. The absence of highly specific markers for MM has served an obstacle for its diagnosis and therapy. We previously produced a monoclonal antibody (mAb) against MM, SKM9-2. We also discovered that SKM9-2 specifically binds to protein HEG homolog 1 (HEG1) that is a novel mucin-like membrane protein. This specificity of SKM9-2 to MM was due to the recognition of HEG1 glycopeptide containing a sialylated glycan. However, there was no mAb that bound to HEG1 glycosylation-independently. We produced new mAbs against HEG1 in this study. Purified partial HEG1expressed in mammalian cells was immunized in mice or rats. After antigen-immunized spleen cells were isolated from mice or rats,the cells were fused with myeloma cells by electrical cell fusion. Hybridomas were screened by ELISA, western blotting orflow cytometry.Through the screening of about 10,000 clones, we obtained more than 10 clones of anti-HEG1 mAb. These antibodies could bind to HEG1 glycosylation-independently. We also obtained two mAbs that can be used in immunohistochemistry. We will investigate the non-glycosylated HEG1expressionin normal tissues.