The rat anti-mouse PD-1 monoclonal antibody (clone No. RMP1-14, rat IgG2a kappa) reacts with the mouse PD-1 protein (CD279 or programmed death-1) encoded by the mouse pdcd1 gene, a member of the CD28 family of the Ig superfamily. PD-1 has two ligands, PD-L1 and PD-L2, both of which belong to the B7 family. It has been shown that in mouse models of melanoma, tumor growth can be transiently arrested via treatment with the anti-mouse PD 1 antibody and the anti-mouse PD L1 antibody which block the interaction between the PD-L1 protein and its receptor PD-1 protein. The RMP1-14 antibody blocks the binding of both the mouse PD-L1 protein and the mouse PD-L2 protein to the mouse PD-1 protein. Our recombinant RMP1-14 antibodies have a part (variable regions) or complete amino acid sequences of the rat anti-mouse PD-1 antibody (hybridoma clone name or number: RMP1-14). The murinized anti-mouse PD-1 recombinant antibody has not only the constant regions of the mouse IgG antibodies but also the murinized variable regions.