Process capability indices (PCIs) have been widely used in the manufacturing industry providing numerical measures on process precision, accuracy and performance. Capability indices measures for processes with a single characteristic have been investigated extensively. However, an industrial product may have more than one quality characteristic. In order to establish performance measures for evaluating the capability of a multivariate manufacturing process, multivariate PCIs should be introduced. In this paper, we analyze the relationship between PCI and process yield. The PCI ECpk is proposed based on the idea of six sigma strategy, and there is a one-to-one relationship between ECpk index and process yield. Following the same, idea we propose a PCI MECpk to measure processes with multiple characteristics. MECpk index can evaluate the overall process yield of both one-sided and two-sided processes. We also analyze the effect of covariance matrix on overall process yield and suggest a solution for improving overall process yield. Copyright © 2013 John Wiley & Sons, Ltd.