The kinetics of the esterification of phthalic anhydride with n-hexanol has been investigated in an experimental isothermal semibatch reactor. The reaction appears to be of a first order with respect to monoester in the presence of sulphuric acid as a catalyst. In the case when tetrabutyl tithanate catalyst is used, the reaction is of the second order with respect to acid and alcohol. The kinetic parameters have been determined.