The flowers of M. velutina were extracted with ethanol to obtain a crude extract that was consecutively extracted using n-hexane, dichloromethane, ethyl acetate and water. The crude extract and fractions were studied for the chemical composition and antioxidant and antidiabetic activities. The extracts had various phytoconstituents, namely steroids, flavonoids, tannins, saponins, alkaloids and glycosides. The aqueous extract had the highest total polyphenol (12.6 mg GAE/g extract) and total flavonoid (205.6 mg QE/g extract) content. The aqueous extract exhibited the strongest antioxidant activities in the ferric reducing antioxidant power assay (EC₅₀ = 4.0 µg/mL), reducing power assay (EC₅₀ = 78.1 µg/mL), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid radical cation assay (EC₅₀ = 48.2 µg/mL), total antioxidant capacity assay (EC₅₀ = 8.7 µg/mL) and 1,1-diphenyl-2-picrylhydrazyl assay (EC₅₀ = 9.3 µg/mL). The aqueous extract showed the strongest inhibitory effect on the activity of α-amylase (IC₅₀ = 376.6 μg/mL) and α-glucosidase (IC₅₀ = 69.7 μg/mL). The results showed that the aqueous extract of M. velutina flowers can be a promising candidate for the control of diabetes and oxidative stress. This is the first report about the chemical components and antioxidant and antidiabetic activities of M. velutina flower extracts.