Four sulfided Ni-W/Al2O3 catalysts were tested in the hydrotreatment of microcrystalline raw paraffin from the dewaxing of heavy neutral oil to obtain high grade paraffin wax. The influence of both reaction conditions (temperature, hydrogen pressure, and space velocity) and catalyst characteristics (tungsten content and porosity) on the properties of the treated paraffins was studied. A similar influence of the operating variables was found for the four catalysts studied. In general, temperatures well above 300 degrees C are needed to obtain transparent and colorless paraffins (Saybolt color >+30); however, rising temperature results in a higher oil content due to cracking reactions. The reaction temperature required to achieve acceptable color values can be reduced by increasing hydrogen pressure, which also reduces paraffin cracking. The rise in the tungsten load of the catalysts from 16.2 to 24.2% (w, WO3 basis) results in higher Saybolt color values, although a simultaneous increase in the extent of cracking reactions takes place and a pressure above 140 kg/cm(2) is required to reduce oil generation. The enhancement in the performance of the catalyst can also be successfully accomplished by increasing simultaneously the porosity and tungsten load of the catalyst, which enables operation at milder conditions of pressure and temperature (40 kg/cm(2), 310 degrees C) while maintaining acceptable Saybolt color and a low content of oil and carbonizable substances.