The rate of hydrolysis of insecticidal O,O-diethyl-α-cyanobenzylideneamino-oxyphosphorothioate (Volaton^ⓡ has been studied in 25% (v/v) aqueous dioxane. On the basis of solvent effect (pH 6.0; m=0.21, n=1.55, pH 12.0; m=0.42, n=3.14 & ｜m｜≪｜ℓ｜), general base catalysis, hydrolysis product analysis, calculation of molecular orbital (MO) and rate equation, it may be concluded that the hydrolysis of Volaton proceeds through the A_(AC)2 mechanism via trigonal bipyramidal (sp³d²) intermediate below pH 7.0, white above pH 9.0 the hydrolysis proceeds through the B_(AC)2 mechanism. Hycrolysis reactivity of Volaton depends on positive charge strength (p≫αC₂) rather than steric hindrance. In the range between pH 7.0 and pH 9.0, these two reactions occur competitively.