Epidemiological studies have shown that regular consumption of fruits and vegetables is associated with reduced risk of chronic diseases. It is recommended to increase consumption of fruits and vegetables to prevent chronic diseases related to free radical-induced oxidative stress. Different varieties of fruits and vegetables provide different vitamins, phenolics, flavonoids, minerals, and dietary fibers for optimal health benefits. Mung bean sprouts are one of the major vegetables in human diet. However, the profiles of phytochemicals and effect of germination on phytochemical content and antioxidant activity of mung bean sprouts have not been studied. The objective of this study was to determine the effect of germination on phytochemical profiles and antioxidant activity of mung bean sprouts. Germination of mung beans dramatically increased vitamin C content in mung bean sprouts in a time-dependent manner and reached the peak on day 8 of germination up to 285 mg/100 g DW, almost 24 times higher than the initial concentration in mung bean seeds (p < 0.05). On fresh weight basis, one serving of mung bean sprouts (about 104 g) provides 21.6 mg of vitamin C, which could meet 36% of Daily Value (DV). In addition, the germination dramatically increased total phenolic compounds and total flavonoids in mung bean sprouts in a time-dependent manner, up to 4.5 and 6.8 times higher than the original concentration of mung bean seeds, respectively. Quercetin-3-O-glucoside content was significantly increased in mung bean sprouts after germination. The total antioxidant activity of mung bean sprouts was increased by 6 times higher than that of mung bean seeds. Therefore, the germination of mung bean sprouts significantly increased phytochemical content, vitamin C content, and antioxidant activity.