Benzoyl chloride (PhCOCl) exhibits a peculiar inhibitve effect on its reaction with some sodium carboxylates (RCOONa) catalyzed by pyridine 1-oxide (PNO) in a CH2Cl2/H2O medium. However, the reaction follows well the rate law-d[PhCOCl](org)/dt = k(obs)[PhCOCl](org) = (k(h) + k(c) [PNO](i,aq))[PhCOCl](org). Where k(h) is the uncatalyzed rate coefficient, k(c), is the catalyzed rate coefficient, and [PNO](i,aq) is the initial concentration of PNO in aqueous phase. When the concentration of RCOONa is the sufficiently high, k(obs) can be expressed as k(obs) = k(h) + k(PNO)[PNO](i,aq)/(1 + k(PNO)). Where k(PNO) is the intrinsic rate coefficient of the reaction between PhCOCl and PNO in CH2Cl2 and k(PNO) is the distribution constant of PNO between H2O/CH2Cl2 phases and is defined as k(PNO)(?)[PNO](aq)/[PNO](org). In order to account for this peculiar phenomenon, the effects of organic compounds, including CCl4, alcohol, ester, and carboxylic acid, were investigated. The presence of organic additive affects the distribution of PNO between H2O and CH2Cl2 phases, the reaction rate, and the yield of product. In general, the value of k(obs) correlated well with the effective concentration of free PNO in the CH2Cl2 phase. For the PNO-catalyzed reaction of PhCOCl and CH3COONa in H2O/CH2Cl2 medium, the main conclusions are:(1) The presence of ROH additive in CH2Cl2 increases the distribution of PNO is CH2Cl2 and the value of k(obs) due to the hydrogen bonding between ROH and PNO.(2) The presence of nonpolar CCl4 and RCOOR＇ in CH2Cl2 decreases distribution of PNO and the values of k(obs).(3) The presence of RCOOH in CH2Cl2 enchances the distribution of PNO in CH2Cl2 and the value of k(obs). However, the main product is PhCOOCOR instead of PhCOOCOCH3 in contrast to the cases of adding ROH, CCl4 and RCOOR＇.The above results have valuable implication in understanding the inhibitive effect of PhCOCl in the PNO-catalyzed reaction of PhCOCl and RCOONa in H2O/CH2Cl2 medium.