Acoustic emission technique was used to monitor the failure modes of multidirectional composite laminates when loaded to 30% of their ultimate. It is shown that each failure mode, that is, fiber fracture, in-plane cracking, and interlaminar cracking, has a different amplitude function when it is presented by normalized parameters. But the discrimination between in-plane matrix cracking and interlaminar matrix cracking is not clear, and another tool is used to discriminate between them, the variation of ring-down period with pulse length. Penny shape artificial delamination also produces unique amplitude distribution that has a smaller slope than the amplitude distribution from free-edge delamination.