The primary objective of this study is to address a key research challenge for improving tradi-tional joint design, which develop functions and structures that can monitor their own structural integrity. A self-sensing technique using the bolt itself to monitor the bearing damage in bolted composite or metallic joints is proposed. The basic concept is based on making Bolt Gauge (BG) measurements. That is, have only to bond a strain gauge onto the surface of bolt head to reflect changes in the bolt strain, which would identify the state of bearing damage. Novel system can maintain not only the peculiar structures and functions of the mechanical fastener, but more importantly, also can provide the self-diagnostic function for component damage. And, it can be contributed directly to technology development for structural health monitoring (SHM) to address these issues, and to meet demanding goals in increasing aerospace vehicle safety and reliability while reducing operating costs. Extensive tests using double lap bolted joint specimen are performed to verify this technique in the various joint cases. The investigations include the effects of the bolt clamp-up, material response, joint geometry and loading history on the detection sensitivities for the bearing damage. The onset and progress of the bearing damage monitored by BG measurements are also compared with acoustic emission (AE) measurements that used in traditional NDE method. A further consideration of the detection mechanisms by BG including an axial loading test and a three-dimensional finite element analysis is performed. The behavior of bolt deformation and stiffness degradation due to the bearing damage initiation and progression are estimated using damage mechanics approach.