The antioxidant activity of Lactuca scariola (Compositae) was investigated by measuring the radical scavenging effect on DPPH (1,1-diphenyl-2-picrylhydrazyl) radical. The methanolic extract of the aerial parts of Lactuca scariola showed strong radical scavenging activity. The EtOAc soluble fraction exhibited a stronger activity than the others, and was purified by silica gel and Sephadex LH-20 column chromatography. Quercetin-3-O-$eta$-D-glucopyranoside, luteolin-7-O-$eta$-D-glucopyranoside, luteolin, quercetin and kaempferol, together with 11$eta$,13-dihydrolactucin were isolated from the EtOAc soluble fraction as active ingredients.