Different solvent extracts of lettuce tree (Pisonia morindifolia R. Br.) and tamarind tree (Tamarindus indica L.) were tested for antioxidant activities. The extracts exhibited effective reducing power and higher radical scavenging efficacy against DPPH and hydroxyl radicals. They also showed metal chelating ability and inhibited peroxidation in the ${eta}$-carotene/linoleic acid emulsion system. The extracts contained considerable levels of vitamin C, vitamin E, total phenolics, tannins, and total flavonoids estimated through standard spectrophotometric methods. As the acetone and methanol extracts of lettuce and tamarind tree recorded pronounced activities, their protective effects in stabilizing peanut oil were tested in terms of their peroxide value, free fatty acid contents, and p-anisidine values in comparison with the synthetic antioxidants butylated hydroxyanisole and butylated hydroxytoluene. Additionally, the antioxidant activity of the extract-treated oil samples and their phenolic contents were monitored to obtain a complete perspective of the influence of the phenolic compounds in oil stability. Results indicated that the selected leafy vegetables, besides acting as good sources of antioxidants, may serve as substitute for synthetic antioxidants in the stabilization of peanut oil.