Interest in mung bean as a functional food is growing. The objective of this study was to characterize the phenolic compounds, antioxidant activities, and antidiabetic activities of black mung beans. Five black mung beans were selected, and one green mung bean was included for comparison. The free phenolic acid and bound phenolic acid contents ranged from 16.68 to 255.51 μg/g and from 2284.53 to 5363.75 μg/g, respectively, whereas the total anthocyanin contents ranged from 0 to 810.55 μg/g with cyanidin-3-glucoside as the most dominant form, respectively. Among the mung beans tested, black mug bean Xiaoqu 7110 had the highest content of bound phenolic acids and exhibited the strongest antioxidant capacities (1,1-diphenyl-2-picrylhydrazyl, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt and oxygen radical absorbance capacity) as compared to the other tested mung beans. Jiheilv 27-3 exhibited higher antidiabetic activities (inhibition of α-glucosidase and advanced glycation end products).