Cogon grass, Imperata cylindrica (L.) Räuschel, was studied for its flavonoid and phenol contents. A series of extracts of the underground (rhizome-root) parts was prepared by hot extraction using solvents of different polarities such as chloroform, methanol, and petroleum ether. The total flavonoid content of the plant extracts was determined based on the reaction with aluminum chloride, sodium nitrite, and sodium hydroxide. Quercetin was used as a standard reference. Chloroform extract showed highest content of flavonoids with 30.88 mg QE/g dry wt., followed by petroleum ether extract which was 22.05 mg mg QE/g dry wt., and methanol extract has the least value with 7.35 mg QE/g dry wt. The total phenolic content of the plant was estimated based on the reaction of Folin-Ciocalteu reagent using gallic acid as the standard reference. Again, the chloroform extract had the highest content with 7.54 mg GAE/g dry wt., while methanol extract contained 5.03 mg GAE/g dry wt., and petroleum ether extract contained 3.63 mg mg GAE/g dry wt. Our study shows that I. cylindrica is a good source of antioxidants.