Objectives: Studies have linked the generation of free radicals with the incidence of degenerative diseases. Antioxidants from plant origin have been proved to play a major role in mitigating against free radicals-induced oxidative damage. This study aimed at assessing the in-vitro and in-vivo antioxidant capability of Psidium guajava leafMethods: The leaves were collected and extracted with 70% methanol. Total phenolic, and flavonoids contents, 2,2-diphenyl-1-picrylhydrazyl and Hydroxyl radicals scavenging activities, and inhibition of lipid peroxidation potential of the extract were assessed. Furthermore, rats (n=21) randomized into three groups were exposed to 50, 150, and 250 mg/kg body weight of the extract for 30 days. Control animals (n=7) received corn oil, after which blood and liver were excised for antioxidant assay.Results: The extract is rich in phenolic and flavonoid compounds. It scavenged DPPH and hydroxyl radicals and inhibits lipid peroxidation in-vitro. In-vivo, it increased the activities of hepatic superoxide dismutase, catalase, glutathione peroxidase, and plasma paraoxonase, and the concentration of hepatic reduced glutathione and MDA.Conclusion: Psidium guajava leaf extract is a potential source of natural antioxidant compounds, capable of supplementing the body's antioxidant defense system
