This study investigated the thermal degradation characteristics of fructose. A 20% fructose solution was heated to 110-150°C for 1-5 hours. Chromaticity, pH, organic acid, 5-hydroxymethylfurfural (HMF), fructose content, electron-donating ability (EDA) (as a percentage), and ascorbic acid (AA) equivalent antioxidant capacity (AEAC) of heated fructose solutions were evaluated. With increasing heating temperature and time, the L-value decreased, and the a- and b-values increased to 120°C for 4 hours and 2 hours, respectively, and then decreased thereafter; however, total color difference increased. The pH and fructose content decreased. Organic acids, such as formic acid, lactic acid, and levulinic acid, and HMF content increased with increasing heating temperature and time. Antioxidant activity increased with increasing heating temperature and time (no antioxidant activity in 20% fructose solution). The EDAs after heating at 130°C for 3 and 4 hours were 17.21% and 31.73%, respectively, and the highest antioxidant activity was 94.57% (150°C for 4 hours). The AEAC was 1.71 mg of AA eq/g before heating and 24.43 mg of AA eq/g after heating at 150°C for 4 hours. These results suggest that heat treatment may be a useful method for increasing the antioxidant activity of fluid foodstuffs such as fruit juices and fructose-containing foods.