The production of benzyl-n-butyl ether from benzyl chloride and n-butanol is studied in phase transfer catalytic system. A third phase is formed when polyethylene glycol (PEG) and dodecane are used as the phase transfer catalyst (PTC) and an organic solvent, respectively. The production rate at the three-phase system is higher by seven times than that at the two-phase system. The ether production rate and its selectivity are dependent on the initial concentration of n-butanol. These are affected by the properties of the third phase, especially the concentrations of n-butanol and water in the third phase. n-Butanol reacts with benzyl chloride and potassium hydroxide simultaneously. The reaction between n-butanol and potassium hydroxide occurs in the aqueous phase. Then, the selectivity of ether on a basis of initial n-butanol is below 0.6 in a stirred tank batch reactor The selectivity is much improved at 0.9 by using a static triphase batch reactor in which the organic and aqueous phases are separated by the third phase. The interphase mass transfer can be accelerated by ultrasonic device. (C) 2001 Elsevier Science B.V. All rights reserved.