A Keggin-type heteropoly acid revealed high catalytic activities for the etherification of diethylene glycol with ethanol to synthesize diethylene glycol ether in the homogeneous phase. The catalytic activities of heteropoly acid were higher than those of conventional acid catalyst such as sulfuric acid and phosphorous acid at the same catalyst concentrations or the same proton concentrations. When a heteropoly acid is used as the catalysts the conversion of the etherification of diethylene glycol with ethanol is 92% and the selectivity for diethylene glycol ethyl ether is 73.5% under the following conditions: the ratio of diethylene glycol to ethanol is 2:1 (mol), temperature is 180-200 degreesC, pressure is 5.0 MPa, the concentration of 12-tungstophosphoric acid is 1.5-2.0% (wt), and the reaction time is 2.5 h. (C) 2004 Elsevier B.V. All rights reserved.