Tungsten-modified ultrastable zeolite catalysts were prepared at three different pHs. Other reference solids were WO3 and a mechanical mixture of 20 wt% WO3 and 80 wt% USY. They were calcined and characterized by surface area measurements (SBET), X-ray diffraction (XRD), acidity and temperature-programmed reduction (TPR). In the incorporation of tungsten to the zeolite, the pH of the impregnation solution controls the cristallinity, the surface area, the acidity of the zeolitic catalysts, the size and the location of tungsten in the USY zeolite and the reducibility.