The decomposition of ammonia is a reaction associated with the process of the nitriding of metals. The kinetics of the ammonia decomposition on iron catalysts has been studied using a differential reactor with internal mixing. The balance between the inlet and outlet ammonia quantity has been used to determine the degree of conversion. The rate of ammonia decomposition could be described by the following expression: r = k(0) exp(E-a/RT)p(NH3). The activation energy of the ammonia decomposition process has been found for samples with potassium as E-a = 96 kJ/mol, for samples without potassium as E-a = 87 kJ/mol.