The kinetics and mechanism for the unimolecular decomposition of o-nitrotoluene (o-CH 3 C 6 H 4 NO 2 ) have been studied computationally at the G2M(RCC, MP2)//B3LYP/6-311G(d, p) level of theory in conjunction with rate constant predictions with RRKM and TST calculations. The results of the calculations reveal 10 decomposition channels for o-nitrotoluene and its six isomeric intermediates, among them four channels give major products: CH 3 C 6 H 4 + NO 2 , C 6 H 4 C(H)ON (anthranil) + H 2 O, CH 3 C 6 H 4 O (o-methyl phenoxy) + NO, and C 6 H 4 C(H 2 )NO + OH. The predicted rate constants in the 500-2000 K temperature range indicate that anthranil production, taking place initially by intramolecular H-abstraction from the CH 3 group by NO 2 followed by five-membered ring formation and dehydration, dominates at temperatures below 1000 K, whereas NO 2 elimination becomes predominant above 1100 K and CH 3 C 6 H 4 O formation by the nitro-nitrite isomerization/decomposition process accounts for only 5-11% of the total product yield in the middle temperature range 800-1300 K. The branching ratio for CH 2 C 6 H 4 NO formation by the decomposition process of CH 2 C 6 H 4 N-(O)OH is negligible. The predicted high-pressure-limit rate constants with the rate expression of 4.10 × 10 17 exp[-37000/T] s -1 for the NO 2 elimination channel and 9.09 × 10 12 exp[-25800/T] s -1 for the H 2 O elimination channel generally agree reasonably with available experimental data. The predicted high-pressure-limit rate constants for the NO and OH elimination channels are represented as 1.49 × 10 14 exp[-30000/T] and 1.31 × 10 15 exp[-38000/T] s -1 , respectively.