The nitration kinetics of 1,2,4-triazol-5-one in 70-100% nitric acid were investigated. Formation of N-nitro-1,2,4-triazol-5-one under these conditions was observed, and its influence on the total process was studied. The activation energies of formation and decomposition of N-nitro-1,2,4-triazol-5-one and of the nitration of 1,2,4-triazol-5-one were determined.