In this work we present experimental information about the effect of feed properties on apparent reaction order and activation energy in the hydrodesulfurization of middle distillates. Experiments were carried out in a pilot reactor at the following operating conditions: reaction temperature of 340, 350, and 360 degreesC; liquid hourly space-velocity of 1.5 and 2.0 h(-1); reaction pressure of 54 kg/cm(2) and hydrogen-to-oil ratio of 2000 ft(3)/bbl. Apparent reaction orders were in the range of 1.70-1.98, while apparent activation energies varied in the range of 14-42 kcal/mol. Reaction orders showed an increase as molecular weight of feed was increased. Activation energies were similar for feedstocks with same reaction order.