Abstract: We consider chemical reactions taking place in micro emulsions, where the mean number of reactant molecules present is small and countable because of small volume of micelles. We describe time evolution of such stochastic reactions and compare the results with traditional chemical kinetics. Petri net modeling and stochastic simulation of α-chymotrypsin catalyzed hydrolysis of p-nitrophenyl acetate in cationic microemulsion has been performed for the first time. The net has been verified using invariant properties of Petri net. A stochastic simulation of the reaction has been carried out using Gillespie hypothesis. The model conclude the nature of a typical enzymatic reaction. The study suggests the concept that enzyme catalyzed reactions in micro emulsions can mimic in vivo enzymatic reactions.