The Taguchi method, a powerful tool to the optimization for quality, is used to improve the mechanical properties of a PCoMo/Al2O3 hydrotreating catalyst in the impregnating and drying processes. An orthogonal array is selected to analyze the effects of the process factors, i.e., impregnating temperature, impregnating time, drying temperature, and drying time. Through this study, not only can the main process factors that affect the mean strength and the Weibull modulus be found, but also the optimal factor levels can be obtained. Results show that the drying temperature is the most significant process factor affecting both the mean strength and the Weibull modulus. It has been shown that the mean strength, Weibull modulus, and mechanical reliability of the hydrotreating catalyst can be improved significantly with the optimization of the impregnating and drying process factors. Experimental results are also provided to confirm the effectiveness of the Taguchi method. (C) 2008 American Institute of Chemical Engineers AIChE J, 54: 3116-3123, 2008