Phytochemical constituents, such as alliin, vitamin C, total phenol and total flavonoid, content of free sugars, and antioxidant activity of 19 garlic lines and cultivars [six parental lines, three controlled cultivars, five cultivars for regional adaptation test (RAT cultivars), and five new cultivars, released by NIHHS for commercialization] cultivated at the experimental field in the NIHHS, RDA in Suwon were evaluated. Average contents of alliin, vitamin C, total phenol and total flavonoid per 100 g dry weight, respectively, were 1,938.4 mg, 9.3 mg, 97.0 mg gallic acid equivalent (GAE) and 16.1 mg catechin hydrate equivalent (CE), and antioxidant activity was 27.5%. Among the three free sugars analyzed, sucrose was present in the greatest quantity (3.48%), followed by fructose (1.05%) and glucose (0.54%). The RAT cultivars, R-01, R-04 and R-05, and new cultivars released for commercialization, NC-02, NC-03 and NC-04, exhibited statistically greater contents of phytochemicals, and consequently possessed higher antioxidant activities as compared to the parental lines and control cultivars. Total flavonoid content showed the highest positive correlations with antioxidant activity (r = 0.908**), followed by total phenol and vitamin C contents.