In this study, the effect of free and bound polyphenolic-rich extract of Syzygium cumini (Linn) Skeels leaf on antioxidant as well as α-amylase and α-glucosidase activities were determined using in vitro model. Polyphenolic-rich extract of Syzygium cumini (Linn) Skeels leaf was prepared accordingly and the capability of the extract to inhibit antioxidants as typified by ferric reducing power (FRAP) and 1,1-diphenyl-2-picryl-hydrazil (DPPH) among other free radicals scavenging abilities were quantified spectrophotometrically, added to this, the activities of (α-amylase and α-glucosidase were also assessed. The bound phenolic extract exhibited more in vitro antioxidant properties as represented by their high radicals scavenging ability in all the free radicals evaluated. Also, the polyphenolic-rich extracts inhibited α-amylase and α-glucosidase, with bound phenolics showing significant (p<0.05) increase in a dose-dependent manner than free phenolics. Therefore, this study suggests the use of Syzygium cumini leaf as a nutraceutical in the management/ control of type II diabetes mellitus patients.