Nitric acid decomposition in mixed acid (an aqueous mixture of nitric and sulfuric acids) was studied from a chemical and a kinetic point of view. The study was focused on the behavior of the reactive mixture in an open system in which the gas formed through the decomposition process can leave the vessel. The reaction network, through which the system could develop, depending on the chemical composition of the mixture and on the temperature, was completely characterized. The data collected indicate that water evaporation can significantly influence the system behavior. Isothermal experiments were carried out to estimate the unknown kinetic parameters through the adoption of a mathematical model able to predict the system behavior at varying process conditions. The proposed model and the estimated parameters were validated through the use of the results collected in a set of experimental runs performed during the nitration of methyl m-nitrobenzoate (3NMB) in mixed acid media. (C) 2013 Elsevier B.V. All rights reserved.