The thermal decomposition of methyl nitrite (CH3ONO), in excess argon, CH3ONO + M → CH3O + NO + M, was studied behind both incident and reflected shock waves. Kinetic data were obtained in the temperature and total pressure ranges 715-1118 °K and 0.8-5 atmospheres, respectively. The reaction was found to be unimolecular in nature and occurring in the low pressure region, with a rate constant expression, k = 1016.36±0.22exp(-30,400 ± 850/RT), cc/mole-sec.; giving the best least-squares fit to the data. Treatment of the data with R.R.K. theory leads to the conclusion that ΔH1OH3O≅ 9.0 kcal/mole rather than the present literature value of 3.5 kcal/mole. The results of previous investigators are compared to the present findings. The molecular absorption coefficient of methyl nitrite at 2800 ± 30 Å was found to be temperature dependent. The values of the absorption coefficient was fit to the form, ϵT3800 ± 30 Å= 636T - 229,010 cc/mole-cm.