The citrus by-products (CBP) released from the citrus processing plants may contain high amount of potential bioactive compounds. Hence, this study aims to evaluate the antioxidant activity of CBP prepared using a novel drying technique known as high speed drying (HSD), economically and efficiently. HSD extract showed high amount or polymethoxylated flavones (heptamethoxyflavone and nobiletin) and flavanone (hesperidin and naritutin). The antioxidant activity was evaluated by means of DPPH, hydroxyl and alkyl radical scavenging assays and lipid peroxidation assay. HSD extract showed strong activities on radical scavenging (IC(50) value of DPPH, hydroxyl and alkyl radicals scavenging were 0.16, 0.5, 0.019 mg/ml, respectively) and lipid peroxidation inhibition. These results suggest that the flavonoids and other phenolic compounds in the HSD extract could be good radical scavengers. Hence, HSD method is an effective and efficient method to transform citrus by-products into dried form and could be used in food and pharmaceutical industry as a natural antioxidant agent. (c) 2008 Elsevier Ltd. All rights reserved.