Causticizing is an important reaction in the kraft pulping process in which white liquor is regenerated from green liquor. In spite of its major significance to the pulp & paper mill, the kinetics of causticizing reaction is not yet well understood. A kinetic model for the causticizing reaction is developed in this study. The model doesn't take into account the mass transfer considerations as the experiments were done with analytical grade lime. The pseudo homogeneous kinetic model developed here is a stiff non-linear differential equation. The parameters involved in the model are solved using Differential Algebraic Optimization Technique. A systematic approach for solving the parameter estimation problem is outlined in this paper. The model predictions were found to be within 1 % of the observed values.