The n-hexane isomerization on Pt/SO42-ZrO2 was studied at 473 K and 6 bar. The catalyst was prepared by adding platinum to zirconium hydroxide by the incipient wetness technique followed by dipping in 0.5 M sulfuric acid solution. Before reaction, the material was calcined and reduced under different conditions. While reduction is unnecessary, the calcination step is very important because it changes the catalytic activity level, The large increase in activity occurs by calcining at 773 K when the material begins to show crystalline structure in X-ray diffraction patterns. The catalytic activity reaches the highest values for calcination between 803 ana 878 K, the selectivity to isomers being almost constant. The crystalline structure is not sufficient to generate an active material, and the catalytic activity is not proportional to the sulfur content and/or the total acidity, A minimum sulfur loading and sulfur species generated by calcination are necessary.