The kinetics of liquid (organic)-liquid (aqueous) two-phase reactions on an immobilized phase transfer catalyst (triphase catalysis) was in vestigated. The displacement reactions of anions (aq. phase) on benzyl bromide or benzyl chloride (org. phase) were carried out at 90°C using tri-n-butylphosphonium chloride bound to 1% cross-linked polystyrene resin as a catalyst. The system was not stirred and all catalyst particles existed at the liquid-liquid interface. The observed sequence of nucleophilic reactivity of anions (CN-∼I->Br-, Cl-) is similar to that in a protic solvent. The reaction of benzyl bromide with potassium chloride was studied kinetically in detail. Under the experimental conditions used. all the mass transfer resistances had no significant effect and the rate of reaction was directly proportional to the amount of catalyst. The reaction order with respect to benzyl bromide was 0.73. From a consideration of the effects of concentrations of both chloride and bromide anions and the reverse reaction, a rate equation was developed.