A physico-chemical model has been formulated to describe the kinetics of the carbothermic nitridation of powder alumina. Based on this model, simultaneous differential equations were derived. When the model was employed to interpret the experimental data, the rate expression of chemical reaction determined in the chemical reaction control region was used and simultaneous differential equations were solved numerically. The expression of effective gas diffusivity, which was left as a fitting parameter to calculate the theoretical predictions, was given by D(eAB)/m2.s-1 = 7.36 x 10(-4) exp (-27.84 kJ mol-1/RT) The correlation between the nonisothermal factor and the half-thickness of the sample as well as correlation between the Sherwood number and the Reynolds number was determined.