The effect of the temperature of calcination of the support on the structural properties of ZrO2 and on the activity of the acid and metal functions of a Pt/WOx-ZrO2 catalyst used in the isomerization-cracking of medium length paraffinic C-8-C-12 Cuts was studied. n-Octane was used as model molecule. The calcination temperature was varied in order to change the metal/acid balance and to increase the yield of the reaction to isoparaffins of high octane number. Four supports were prepared by impregnating Zr(OH)(4) with ammonium metatungstate (15% W) and then they were calcined at 500, 600, 700, and 800 degrees C. These supports were then impregnated with H2Cl6Pt(1% Pt) and calcined in air at 500 degrees C. They were characterized by means of chemical analysis, XRD, N-2 adsorption, pyridine TPD, hydrogen chemisorption, temperature-programmed reduction, and infrared spectroscopy of adsorbed CO. The catalytic activity of the catalysts was evaluated with the test reactions of n-octane (300 degrees C, 1 atm, WHSV= 1, H-2/n-C-8=6), n-butane (350 degrees C, WHSV= 1, H-2/n-C-4=6), and cyclohexane (300 degrees C, 1 atm, WHSV =12.6, H-2/CH=1.4). The results reveal a strong influence of the calcination temperature on the final metal/acid balance of the catalysts. At 5 min time on stream, all catalysts produce a RON gain of 55 points. In general, the higher the calcination temperature the higher the promoting action of W for generating strong acid sites and the higher the concentration of Pt delta+ of the metal function. The highest liquid yield and isoparaffin yield were obtained with the sample calcined at 700 degrees C. The sample calcined at 800 degrees C had the highest cracking activity and the maximum yield of isobutane and propane.