Process capability index pk C is the most widely used index in making managerial decisions since it provides bounds on the process yield for normally distributed processes. However, existent methods for assessing process performance which constructed by statistical inference may unfortunately lead to fine results, because uncertainties exist in most real-world applications. Thus, this study adopts fuzzy inference to deal with testing of pk C . A brief score is obtained for assessing a supplier’s process instead of a severe evaluation. Keywords—Process capability analysis; quality control.