Process capability indices (PCIs) are very useful statistics to summarize process" distribution and width. They are one of the resit lts of process capability analysis. This analysis is based on normal distribution approximation which is used to calculate the probability of the process to produce between and out of specification limits. In this paper, process ability which is defined as produce conforming items is analyzed by taking fuzzy normal distribution into account. Mean, standard deviation and specification limits are defined as triangular and trapezoidal fuzzy numbers, respectively. Then fuzzy probabilities of conforming and nonconforming items are calculated. © 2008 IEEE.