A new sequential method to estimate rate constants in complex kinetic models is proposed. This method reduces the number of parameters to be estimated simultaneously. A five-lump kinetic model for the catalytic cracking process was selected in order to apply the proposed methodology. The kinetic parameters of this model were determined by using successively non linear estimation with various three-and four-lump kinetic models. Experimental data obtained in a MAT reactor using three gas oils and a commercial equilibrium catalyst were utilized to evaluate the rate constants. The effects of reaction temperature and space velocity were studied in the range of 480-500 degreesC and 6-48 h(-1), respectively. Good predictions of gas oil, gasoline, LPG, dry gas; and coke yields were obtained from the kinetic model, with average absolute deviation less than 2% with respect to experimental information.