The localization of microcracks in unnotched concrete specimens under uniaxial tension was studied using acoustic emission (AE) analysis techniques. A new method was developed to locate the source of the AE events. It was found that the AE events started to concentrate on a narrow band of the specimen when the load reached about 80 percent of the peak value. The macro deformation of the specimen was also monitored using four LVDTs uniformly distributed along the direction of tension. Based on the experimental observations, the relationship between the occurrence of AE events (microcracking) and macro deformation was further investigated. It was found that the localization of microcracks controlled the development of the macrocrack in the specimen.