The kinetics of the neutral hydrolysis of ethylchloroformate have been studied in water-acetonitrile and in water- tetrahydrofuran mixtures in the temperature range of 30-50-degrees-C. The hydrolysis reaction follows a first-order rate law. The rates of the hydrolysis showed maxima at 0.9 and at 0.92 water mole fraction in water-acetonitrile and in water- tetrahydrofuran mixtures, respectively. The activation parameters DELTA-H# and DELTA-S# showed minima at nearly the same solvent composition range. The significance of these results from the viewpoint of the changing of solvent structure in such mixture is discussed.