The antioxidant properties and effect of essential oil of black pepper (Piper guineense) seeds on α -amylase, α -glucosidase (key enzymes linked to type-2 diabetes), and angiotensin-I converting enzyme (ACE) (key enzyme linked to hypertension) were assessed. The essential oil was obtained by hydrodistillation and dried with anhydrous Na2SO4, and the phenolic content, radical [1,1-diphenyl-2 picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and nitric oxide (NO)] scavenging abilities as well as the ferric reducing antioxidant property (FRAP) and Fe(2+)-chelating ability of the essential oil were investigated. Furthermore, the effect on α -amylase, α -glucosidase, and ACE enzyme activities was also investigated. The characterization of the constituents was done using GC. The essential oil scavenged DPPH∗, NO∗, and ABTS∗ and chelated Fe(2+). α -Pinene, β -pinene, cis-ocimene, myrcene, allo-ocimene, and 1,8-cineole were among the constituents identified by GC. The essential oil inhibited α -amylase, α -glucosidase, and ACE enzyme activities in concentration-dependent manners, though exhibiting a stronger inhibition of α -glucosidase than α -amylase activities. Conclusively, the phenolic content, antioxidant activity, and inhibition of α -amylase, α -glucosidase, and angiotensin-1 converting enzyme activities by the essential oil extract of black pepper could be part of the mechanism by which the essential oil could manage and/or prevent type-2 diabetes and hypertension.