The positron lifetime and DSC measurements for EBBA have been made with heating and cooling clycles. The experimental results show that the shorter lifetime (τs) is essentially independent of temperature while the longer lifetime (τ1) and the intensity (I1) change abruptly twice with temperature. These two critical temperatures are in accordance with "he transition temperature measured by the DSC. In the heating and cooling clycles the transition temperature are different. The changes in microstructure during the phase transition have been explained by the ORE model of positron annihilation, which raised the idea that positron can be a probe in the study of EBBA phase tyansitioa