Resistance to burning is one of the most useful properties that can be imparted to leather. Pyrovatex CP is rich in phosphorus and nitrogen and has been successfully used as a flame-retardant agent in the presence of etherified methylolated melamine (EMM). The effects of a finishing formulation containing Pyrovatex CP and EMM on the flame retardancy and other properties of modified leather have been studied under different conditions. The synergistic effect of the N/P ratio has been thoroughly investigated through the estimation of the nitrogen and phosphorus contents, and their impact on the flame retardancy, tensile strength, and elongation at break of the treated leather has been studied. An investigation of the different factors has led to the following conclusions: (1) the P and N percentages increase with increasing curing temperature and time, (2) increases in the Pyrovatex CP and EMM concentrations are accompanied by an enhancement of the P and N percentages, and (3) all samples exhibit loss in their tensile properties but within an acceptable range (20%).