Abstract: The present study was carried out to evaluate the antioxidant capacity of the 95% ethanol crude extracts and their four solvent fractions( petroleum ether,ethyl acetate,normal butyl alcohol and aqueous) of Rubia tibetica Hook.F. The extracts of the Rubia tibetica Hook. F. were evaluated for their total phenols,total flavonoids and antioxidant activity( DPPH radical,ABTS radical,hydroxyl radical,superoxide scavenging effect,reducing power and ferrous ions chelating activities). The relationship between the antioxidant activity and the content of total phenolics and total flavonoids was analysed.The results showed that all the fraction except water fraction had great antioxidant activity and the content of total phenolics and total flavonoids had a highly significant correlation with the activity.The ethyl acetate fraction was the most effective fraction with the highest content of total phenolics and total flavonoids and the content of them were( 232.03 ± 1.74) mg rutin equivalent / g extract and( 173.53 ± 1.75) gallic acid equivalent mg / g extract,respectively. The EC50 values of ethyl acetate fraction based on DPPH,superoxide,hydroxyl radical and ABTS was 0.06 ± 0.01,0.17 ± 0.01,( 0.24 ± 0.02) mg / m L and( 1.75 ± 0.23) μg / m L. The EC50 of ethyl acetate fraction on ferrous ions chelating activities was( 0.11 ± 0.01) mg / m L. Ethyl acetate fraction of Rubia tibetica Hook.F,a strong ability to act as antioxidant,may be considered as a natural source of active compounds.