This study was performed for the purpose to investigate the applicability of the Acoustic Emission (AE) technique to determine in-situ stresses and, to some extent, to clarify the controversial issues related to this technique given in literature. By taking into consideration the results from previous studies, it was decided to give prime consideration to the contreversial aspects of the subject and to perform AE experiment under uniaxial loading conditions on specimens which were pre-loaded in laboratory. For the purpose, different types of rock samples were collected and mortar samples were prepared. After some geomechanical properties of these samples were determined, deformation and crack propagation stages were identified for each sample group. On the basis of these stages, the pre-stress levels selected were applied to the specimens under uniaxial and triaxial conditions. Just after the pre-loadings, AE experiments under uniaxial loading conditions were carried out on these specimens and Kaiser Effect (KE) levels were determined. In addition, rock core samples were obtained from boreholes drilled in previous years and the AE experiments were also carried out on these samples. The results of the tests were evaluated based on some theoretical and emprical approaches, and it was concluded that the KE levels determined from the AE experiments under uniaxial loading conditions were related to, not only the axial pre-stresses affecting the rock samples, but also the lateral pre-stresses and microcracks involved by the test samples. According to these findings, some equations of which KE levels could be expressed were suggested. These studies and some of those in literature revealed that the results from the approach, that "the KE levels determined from AE experiments under uniaxial loading conditions on cores, which are extracted from oriented block samples, can be used to determine in-situ stresses (pre-stresses) acting on the test sample in the direction of uniaxial loading", are open to discussion.