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 Unfolding process of Concanavalin A under TFE. The Concanavalin As in pH2 hydrochloric acid gives a CD spectrum specific to -sheet structure. In contrast, in a solution with 50% of TFE added it has a CD spectrum specific to -helix structures. As seen in Figure 1, a big change from abundant -sheet JASCO圓二色光譜儀CD J-1500