In this work, a study about the separation of antioxidant substances from Siraitia grosvenori' leaves considered as an agricultural waste was undertaken. The leaves of S. grosvenori were extracted with ethanol (phi(B) = 0.95) to obtain a crude extract (SEE). The antioxidant activity of SEE was evaluated and compared with that of butylated hydroxytoluene (BHT) using DPPH free radical, ABTS free radical, total antioxidant activity and reducing power assay. SEE had an antioxidant activity similar to that of BHT. The total flavonoids content of SEE was found to be catechin equivalent of 83.45 g kg(-1) of extract. Higher flavonoids compounds may be major contributors to its high antioxidant activity. Following activity-oriented separation, three flavonoid compounds such as kaempferol-3-O-alpha-L-rhamnopyranosyl-7-O-[beta-D-glucopyranosyl-(1-2)-O-L-rhamnoside] (GR), kaempferol-3-O-beta-D-glucose-7-O-alpha-L-rhamnoside (KG) and quercetin were separated from S. grosvenori' leaves. All of them expressed good free radical scavenging activities. (C) 2011 Elsevier Ltd. All rights reserved.