We evaluated antioxidant activities of heated pear juice (HPJ) exposed to 120, 130, and $140^{circ}C$ for 2 hr. HPJ was partitioned using n-hexane, chloroform, ethyl acetate, n-butanol, and water. The ethyl acetate fraction treated at $130^{circ}C$ for 2 hr showed strong antioxidant activity; thus, this extract was isolated and purified using silica gel column chromatography and preparative high performance liquid chromatography. The structure of the purified compound was determined using ultraviolet and mass spectrometry, $^1H$-nucelar magnetic resonance (NMR), and $^{13}C$-NMR. Antioxidant activities of the isolated compound were evaluated and compared with ${alpha}$-tocopherol, ascorbic acid, and butylated hydroxytoluene (BHT) using DPPH and ABTS assays. The isolated compound was identified as 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP). The DPPH radical-scavenging activity ($IC_{50}$) of DDMP occurred in the following order: ascorbic acid ($45.3{mu}g/mL$) > ${alpha}$-tocopherol ($69.2{mu}g/mL$) > DDMP ($241.6{mu}g/mL$) > BHT ($268.0{mu}g/mL$). Furthermore, DDMP showed strong ABTS radical-scavenging activity (569.0 mg AA eq/g).