The esterification kinetics of phthalic anhydride with ethanol was investigated in the isothermal reactor in the presence of sulfuric acid catalyst. The values of reaction rate have been determined on the basis of empirical equation describing experimental data. The calculated values of reaction rate were introduced into kinetic equation to estimate appropriate parameters. The investigations were carried out for three initial substrate molar ratio: (phthalic anhydride-ethanol) 1:3,1:5,1:6.