Studies on the peptide fibers have traditionally focused on investigating their morphological properties, with insufficient attention paid to their physical characteristics, such as thermal stability. This study aims to address this gap by designing several types of peptide nanofibers with α-helical structures and investigating their thermal responses. It was shown that one of the peptides had a transition temperature close to 130 ºC, which is exceptionally high for a biomolecule. Additionally, some peptides exhibited liquid crystal-like thermal transitions, in which multiple molecules underwent a simultaneous structural transition. We attempted to elucidate the factors behind these rare phenomena through thermodynamic analyses. The findings from this study are expected to pave the way for the development of artificially designed α-helical fibers.