A phytochemical investigation on the methanolic extract of Cosmos caudatus has led to the isolation of quercetin $3-O-{eta}-D-arabinofuranoside$ (1), quercetin $3-O-{eta}-D-rhamnoside$ (2), quercetin $3-O-{alpha]-D-glucoside$ (3) and quercetin (4). These compounds were shown to be the antioxidative constituents of the plant when evaluated using the ferric thiocyanate (FTC) and thiobarbituric acid (TBA), and radical scavengers based on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays.