<p>The aminolysis and hydrolysis reactions for profenofos have been comprehensively investigated by using the B3LYP/6–311 +  + G(<i>d,p</i>), M06-2X/6–311 +  + G(<i>d,p</i>) and MP2/6-311G(<i>d</i>) theoretical levels. Three possible mechanisms, namely the P–OR, P–SC₃H₇ and P–OEt decomposition channels, are systematically evaluated, each via both the concerted and stepwise pathways. Additionally, the effect of solvent water is also simulated by adopting PCM model at M06-2X/6–311 +  + G(<i>d,p</i>) level. Our results convincingly demonstrate that the first step of stepwise mechanism acts as the rate-determining stage, exhibiting significantly higher energy barrier than the second one. For the aminolysis reaction, the stepwise of P–OEt decomposition pathway is identified as the most favorable. Furthermore, the calculations clearly suggest that the stepwise channel for hydrolysis is also more prominent than the concerted mechanism. The energy barriers for the concerted hydrolysis reactions are notably higher than those for the corresponding aminolysis reactions. In addition, the solvent effects have no remarkable influence on the reaction mechanisms. These findings provide valuable insights into the degradation behavior of profenofos and provide useful information for understanding the reactivity of organophosphorus pesticides.</p>