The rat anti-mouse PD-L1 monoclonal antibody 10F.9G2 (rat IgG2b kappa) reacts with the mouse PD-L1 protein (programmed death ligand-1, B7-H1 or CD274), a member of the B7 family of the Ig superfamily. PD-1 has two ligands, PD-L1 and PD-L2. It has been shown that in mouse models of melanoma, tumor growth can be transiently arrested via treatment with the anti-mouse PD-1 and anti-mouse PD-L1 antibodies which block the interaction between the PD-L1 protein and its receptor PD-1 protein. The 10F.9G2 monoclonal antibody blocks the binding of the mouse PD-L1 protein to the mouse PD-1 protein. Our recombinant 10F.9G2 antibodies have a part (variable regions) or complete amino acid sequences of the rat anti-mouse PD L1 monoclonal antibody (hybridoma clone name or number: 10F.9G2).