To develop a functional juice using garlic (Allium sativum L.), heated garlic juice was investigated using a central composite design set with variables of treatment temperature (110, 115, 120, 125, and $130^{circ}C$) and time (1, 2, 3, 4, and 5 hr) using high temperature and pressure treatment apparatuses. Total soluble solid, total acidity, reducing sugar, total pholyphenol contents, electron donating activity (EDA), and ascorbic acid equivalent antioxidant capacity (AEAC) in heated garlic juice were increased with increasing heating temperature and time. The highest total soluble solid content was $17.81;^{circ}brix$ at $123.10^{circ}C$ for 1.10 hr. The highest total acidity was 1.43% at $127.35^{circ}C$ for 4.35 hr. The highest reducing sugar content was 86.67 mg/mL at $119.90^{circ}C$ for 4.35 hr. The highest total polyphenol content was 8.42 mg/mL at $127.75^{circ}C$ for 4.26 hr. The highest EDA and AEAC were 60.09%, and 7.40 mg AA eq/mL at $127.85^{circ}C$ for 4.23 hr, and $128.10^{circ}C$ for 4.18 hr, respectively.