It is well known that mechanisms of fracture and crack growth depend upon material characteristics such as fracture toughness, environmental condition, cracd geometry and mechanical properties. It seems to be very important to investihate the effects of the above factors on the behavior of structural components which contain flaws for the detailed evaluation of their intehrity. In this experimental research, fracture behaviors of moterials were investigated by using Acoustic Emission(AE) technique. The fracturing processes of materials were estimated through both the tension specimens. For the detrmlnatlon of yied strength or fracture toughness, the critical applied load at the crack initiation and propagation is thought to be very important. The critical applied load(PQ) was determined through AE signal. The source of AE signal was estimated by fractography analysis. These experimental results may contribute to the safety analyses and the evaluation of strength of structures.