An opportunity to use the elevated temperature has been recently increasing in various elements of heat facilities or machines such as heat exchanger tubes, pressure vessels, engines of aircraft, boilers and turbines in power plants, and nuclear reactor components, etc. as machinery industry develops. Thus, the development of such elevated-temperature heat-resisting materials and the studies on their elevated-temperature materials friction welding, creep design and analysis have been considered as an important and needful fact. In this paper, friction welding optimization for 1Cr0.5Mo to STS304 and AE applications for the weld quality evaluation were investigated. The important results of this study are as follows : The techniques for dissimilar friction welding optimization of the elevated temperature materials 1Cr0.5Mo and STS304 and its real-time weld quality evaluation by AE were developed, considering on both strength and toughness. Quantitative relationship was identified among welding condition, weld quality and cumulative AE counts.