A quantitative method of analyzing the ability of sake to scavenge 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) was established and applied to sake during storage. The DPPH-scavenging ability of sake was found to decrease non-enzymatically dependent on the Length and/or temperature of storage, but the decrease gradually leveled off. From the rate constant of the initial decrease in DPPH-scavenging ability, the Arrhenius activation energy was calculated to be 15.8 kcal/mol. The decrease in the DPPH-scavenging ability of sake is considered to be attributable to the generation of free radicals. These findings suggest that DPPH-scavenging ability can be utilized as an index to describe the sensory maturation of sake that will complement other maturation indexes such as 3-deoxyglucosone and Absorbance (420 nm). The decrease in the DPPH-scavenging ability of sake correlated significantly (p < 0.01) with sensory evaluations of the maturation.