Abstract: A mixed kinetic model with a computer program has been proposed for the processing of the hydrodesulphrisation and hydrodenitrogenation experimental data, which can not be treated by first order or pseudo-second order kinetics. A brief review of the authors pseudo-second order kinetic model is also presented. In the pseudo-second order kinetic model a hyperbolic function of type is used to describe the experimental conversion level - reciprocoal of LHSV curves. By defining the extreme value of conversion level Ym under certain operating conditions and catalyst as Lim Y=1/b, it is possible to trans- form the above function to the following pseudo-second order kinetic equation: where and the following model equation is obtained: The predicted values of % conversion are in good agreement with the experimental values. In the case when b<1, the model fails to describe the behaviour of conver-sion curves kinetically, so a mixed kinetic model is developed by assuming both the first and second order reactions can take place on the catalyst simultaneously. Thus the following kinectic equation is obtained: The rate constants K1 and K2 can be found on a computer by preassuming a series of K2/K1 ratio and K1 values and then minimizing the sum of squares of the difference between experimental and predicted values of Y. Generally the mixed kinetic model can be used for a broad range of kinetic data in hydroprocessing. However, in the case of b>l,the pseudo-second order kinetic model seems to be preferred.