Mutations of isocitrate dehydrogenase 1/2 (IDH1/2) produce oncometabolite R(-)-2-hydroxyglutarate in several tumors. Arginine 132 (R132) of IDH1 and arginine 172 (R172) of IDH2 are functionally important residues. Although MsMab-1 monoclonal antibody (MAb), which is multi-specific for mutated IDH1/2, has been established, MsMab-1 does not react with all IDH1/2 mutations. Herein, we immunized rats with IDH1-R132L peptide, and screened IDH1-R132L-reactive/IDH1-wild-type non-reactive MAbs in enzyme-linked immunosorbent assay. Unexpectedly, the newly established MsMab-2 MAb recognized not only IDH1-R132L but also IDH2-R172M in Western blot analyses, neither of which was detected by MsMab-1. Taken together, the combination of MsMab-1 and MsMab-2 could be useful in diagnosis of mutated IDH1/2-bearing tumors.