Disclosed is a method of determining whether a temperature of a sample has reached a predetermined temperature. The method comprises the steps of: mixing an albumin-containing sample with a peptide reagent comprising a peptide for temperature determination； heating the mixture； detecting an optical change of the mixture； and determining whether the temperature of the mixture has reached the predetermined temperature based on the detection result of the optical change. In the method, a dissociation constant (Kd) of binding of the peptide for temperature determination to albumin is 500 μM or more, and the peptide for temperature determination comprises a first labeling substance and a second labeling substance.
