The aim of the present study was to quantify phenolic acids and flavonoids from Citrullus colocynthis roots (CCR), leaves (CCL) fruits (CCF) and compare the antioxidant and free radical scavenging activities of their extracts and major compounds. Reverse phase high performance liquid chromatography method was developed and validated for the simultaneous quantification of phenolic acids and flavonoids from ethanol and hexane extracts of CCR, CCL and CCF. The antioxidant activity of CCR, CCL and CCF extracts was investigated by measuring total phenolics, total flavonoids contents, DPPH free radical scavenging activity, inhibition of linoleic acid peroxidation and reducing power. The RP-HPLC analysis of C. colocynthis extracts revealed the presence of ferulic acid, vanillic acid, p-coumeric acid, gallic acid, p-hydroxy benzoic acid and chlorogenic acid being the major phenolic acids and quercetin, myricetin and catechin being the most prominent flavonoids compounds. The amounts of TP (3.07-18.6 mg/g of dry plant material, measured as gallic acid equivalent) and TF (0.51-13.9 mg/g of dry plant material, measured as catechin equivalent) were higher in ethanol extracts of CCL, followed by CCR and CCF. Ethanol extract of CCL exhibited the highest antioxidant and DPPH radical scavenging activities followed by ethanol extracts of CCR and CCF. However, only hexane extract of CCF showed considerable DPPH radical scavenging activity. The results suggested that CCR, CCL and CCF extracts showed a wide variability of their phenolic acids and flavonoids composition and antioxidant activity. (C) 2013 Elsevier B.V. All rights reserved.