Sintering kinetics and densification behavior of pure ThO2 have been studied using high temperature dilatometer experiments at constant rate of heating. Sintering activation energy has been determined by Wang and Raj method. Master sintering curve (MSC) for densification is a functional sintering model that describes densification under arbitrary time temperature excursion of a particular material during sintering. MSC for pure ThO2 has been constructed by fitting experimental relative density versus work of sintering data with modified sigmoid function. Five independent parameters of the fitting function are determined by Nelder-Mead optimization technique with the objective of minimizing fitting error in terms of mean residual square. A FORTRAN program has been developed for efficient construction of best converged master curve. It is shown that activation energy of pure ThO2 found by MSC approach is consistent with those obtained by other methods.