The heat capacities (C-p) of sequenced polytripeptides, (prolyl-prolyl-glycine)(10) and (prolyl-hydroxyprolyl-glycine)(10), were measured, The peaks in the C-p curves associated with thermal transitions were observed to shift significantly without changing their shapes. The observed transitions are discussed in the framework of a first-order phase transition. The cause of the origin of the widths of the observed transitions is also discussed in relation to the Gibbs phase rule.