Metamorphic proteins switch reversibly between distinctly different folds often with different functions under physiological conditions. Here, the kinetics and thermodynamics of the fold-switching at different temperatures in a metamorphic protein, KaiB, involved in cyanobacterial circadian clock, reveal that enthalpy-driven the fold-switching to form fold-switched KaiB (fsKaiB) and the fsKaiB and ground-state KaiB (gsKaiB) are more dominantly at lower and higher temperatures, respectively. Thermodynamic analysis indicates that conformational and solvent entropy have opposing effects on KaiB's fold-switching. The folding kinetic reveals that as KaiB folds, it preferentially folds into gsKaiB and then switches fold to fsKaiB. Temperature-sensitive protein fold-switching can be further extended into applications, such as new temperature-sensitive molecular switcher and biosensors development.