In this study, reaction model and reactions rate accelerated by o-iodosobenzoate ion(IB⊖) on hydrolysis reaction of p-nitrophenyl valate(NPV) using ethyl tri-octyl ammonium mesylate(ETAMs) for quaternary ammonium salts, the phase transfer catalysis(PTC) reagent, were investigated. The effect of IB⊖ on hydrolysis reaction rate constant of NPV was weak without ETAMs solutions. Otherwise, in ETAMs solutions, the hydrolysis reactions exhibit higher first order kinetics with respect to the nucleophile, IB⊖, and ETAMs, suggesting that reactions are occurring in small aggregates of the three species including the substrate(NPV), whereas the reaction of NPV with OH⊖ is not catalyzed by ETAMs. Different concentrations of NPV were tested to measure the change of rate constants to investigate the effect of NPV as substrate and the results showed that the effect was weak. This means the reaction would be the first order kinetics with respect to the nucleophile. This behavior for the drastic rate-enhancement of the hydrolysis is referred as 'Aggregation complex model' for reaction of hydrophobic organic ester with o-iodosobenzoate ion(IB⊖) in hydrophobic quarternary ammonium salt(ETAMs) solutions.