Anti-calcyclin binding protein (CacyBP) monoclonal antibodies (MAb) were produced using an in vitro immunization method. BALB/c mouse splenocytes were immunized with purified 6 x His-CacyBP fusion protein and fused with myeloma cells using polyethylene glycol (PEG) 4000. By selection using enzyme-linked immunosorbent assay (ELISA), three anti-CacyBP MAbs were obtained. The MAb BD1, whose isotype was IgG1, interacted with the fusion protein. Western blot and immunofluorescence microscopy showed that the MAb BD1 against CacyBP could recognize CacyBP protein derived from human gastric cancer cell lines in both native and denatured forms. This MAb would act as a useful tool for the detection of CacyBP protein in future studies.