The kinetics of the acidic nitrosation of 5-methylresorcinol (MR), the main component of oil shale originated phenols, has been studied. Formation of 2,4-dinitroso-5-methylresorcinol was followed by an increase in optical density and temperature of the reaction mixtures over the initial concentrations of the reagents 1.10(-4)-0.05 mol/L and over the acidities pH 4.38-1.5 mol/L of H2SO4. The kinetic model for the two-step consequent-parallel nitrosation was approximated to the second-order rate equation. The apparent rate constant was revealed as the result of three rate constants for the contributing nitrosation reactions of MR with HNO2, H2NO2+ and of the proton-catalysed reaction with H2NO2+. The constants K-1 and K-2 for the two-step protonisation of NO2- were determined.