We have studied the effect of 31 extracts and 10 components from some edible and medicinal plants on the formation of lipid peroxide in the liver homogenate of rat in vitro. The 70% acetone extracts of Allium tuberosum, Beta vulgaris var. cicla and Brassica juncea var. integrifolia, and methanol extract of Capsicum annuum decreased the formation of lipid peroxide by 33%, 58%, 62% and 56% at the concentration of 1mg/ml, respectively. And these four extracts inhibited the lipid peroxidation at the concentration of $10^{-1}$mg/ml by 17%, 46%, 49% and 45% respectively. Among the component tested, quercetin, quercitrin and isorhamnetin reduced the formation of lipid peroxide by 45%, 15% and 28% respectively at the concentration of $10^{-2}$mg/ml.