We have investigated the decomposition kinetics of imidazole, 2-nitroimidazole, and 4-nitroimidazole using TG-DTA technique under nitrogen atmosphere. Isoconversional methods were used for the evaluation of kinetic parameters from the kinetic data of different heating temperatures. The Friedman method provided comparably higher values of activation energy than the Flynn-Wall-Ozawa method. Imidazole, 2-nitroimidazole, and 4-nitroimidazole were decomposed by the multistep reaction mechanism evident from the nonlinear relationship of activation energy and the conversion rate. The NO2 elimination and nitro-nitrite isomerization are expected to be competitive reactions in the decomposition of 2-nitroimidazole and 4-nitroimidazole. The present study may be helpful in understanding how the position of NO2 group affects the decomposition kinetics of substituted imidazoles.