AE and thermal expansion of both stressed and unstressed Oshima granite were investigated. The samples were subjected to slow cyclic temperature change (0. 5 K/min) between 290K and 370K or between 210K and 290 K. A large number of AE events occurred only during the first cycle both heating and cooling. Under unstressed conditions, the thermal expansion coefficient became highly temperature dependent when the occurrence of AE events was observed. When the rock was subjected to thermal cycling under uniaxial stress conditions, the thermal expansion coefficient in the axial (loading) direction became temperature independent, while that in the circumferential direction was unchanged. The reactivation of the AE events was observed during the first heating after the removal of stress. These observations suggest that microcracks are produced by the mismatch of thermal expansion of individual mineral grains and cause the temperature dependency of the thermal expansion coefficient of Oshima granite. The anisotropy of thermal expansion observed when the samples were uniaxially compressed, is explained by the closure of microcracks perpendicular to the axial direction. © 1986, The Society of Materials Science, Japan. All rights reserved.