The Stopped Flow method is used to analyze reactions occurred during the duration of several milliseconds and several seconds meanwhile the CD measurement provides valuable information regarding the proteins secondary structures and environment of aromatic amino acids. Therefore, CD measurement with Stoppedflow method provides one of the best techniques in analyzing the proteins Unfolding and Refolding process. Concanavalin A (derived from Jack bean) in natural state has abundant -sheet structures, however, it is known that its structure changes into the one with rich -helix under trifluoroethanol (TFE) and its Unfolding process has been reported also. In this application, the model SFS-492 High-Speed Stopped-flow System was used to measure the Unfoldin JASCO圓二色光譜儀CD J-1500