A 2-Tiobarbituric acid (TBA) reaction is widely used to measure the degree of lipid peroxiation such as in salmon oil, soybean oil, and liver homogenate. We attempted to measure the staling of sake by using a TBA reaction.Visible spectra of the reaction mixture of sake stored at high temperatures with a TBA reagent were more highly colored than that of sake in cool storage. A red pigment, which was similar to product of the TBA reaction with malonaldehyde, was isolated from the reaction mixture of sake stored at high temperatures with a TBA reagent by HPLC. The quantity of red pigment can be measured by absorbance at 530 nm of the reaction mixture. The red pigment increased with storage time, and temperature of the sake. This suggests that a TBA reaction can be use to measure the staling of sake.