Nano-modification is an effective method currently used to improve mechanical properties of concrete by adding various nanomaterials. The results obtained from previous studies demonstrate that presence of these particles has positive effects on both mechanical and durability performances of concrete. However, while the existing studies investigate the state of resistance, revealing progressive failure mechanism of nano-particle added concrete under loading is a significant subject. In this regard, Acoustic Emission (AE) method is useful for identification of invisible damage progress by means of basic phenomenon defined as release of energy due to a fracture and propagation of it as elastic waves in a stressed medium. Apart from the existing studies in the literature, this paper is focused on investigation of the influences of nano-clay on mechanical and failure behaviors of concrete by AE. For this purpose, a plain and three different concrete mixtures including 1%, 3% and 5% nano-clay (NC) of cement weight were prepared. 100x100x600 mm beam specimens were produced from these mixtures and were tested under three-point-bending. Furthermore, to reveal invisible failure mechanisms of the specimens, all tests were simultaneously monitored with AE method. The results reveal that presence of nano-clay increases the load capacity and ductility of the concrete specimens which is also confirmed by AE results, as more amount of micro-scale events are obtained.Nano-modification is an effective method currently used to improve mechanical properties of concrete by adding various nanomaterials. The results obtained from previous studies demonstrate that presence of these particles has positive effects on both mechanical and durability performances of concrete. However, while the existing studies investigate the state of resistance, revealing progressive failure mechanism of nano-particle added concrete under loading is a significant subject. In this regard, Acoustic Emission (AE) method is useful for identification of invisible damage progress by means of basic phenomenon defined as release of energy due to a fracture and propagation of it as elastic waves in a stressed medium. Apart from the existing studies in the literature, this paper is focused on investigation of the influences of nano-clay on mechanical and failure behaviors of concrete by AE. For this purpose, a plain and three different concrete mixtures including 1%, 3% and 5% nano-clay (NC) of cement weight were prepared. 100x100x600 mm beam specimens were produced from these mixtures and were tested under three-point-bending. Furthermore, to reveal invisible failure mechanisms of the specimens, all tests were simultaneously monitored with AE method. The results reveal that presence of nano-clay increases the load capacity and ductility of the concrete specimens which is also confirmed by AE results, as more amount of micro-scale events are obtained.