The objective of the present study was to compare fresh (F) use and the effects of boiling (B) and deep-fat frying (DF) on the leaf of Citrus hystrix on total phenolic content, the types and amounts of flavonoids and their total antioxidant capacities (TAC), as measured by three different assays: oxygen radical absorption capacity, ferric reducing/antioxidant power, and scavenging effect on the 2,2-diphenyl-1-picrylhydrazyl free radical. Boiling decreased TAC values on the three assays. The amount of total flavonoids calculated as aglycone equivalents of eight identified flavonoids (cyanidin, myricetin, peonidin, quercetin, luteolin, hesperetin, apigenin and isorhamnetin) determined by high-performance liquid chromatography was 1,129 (DF), 1,104 (F) and 549 (B) mg/100 g freeze-dried weight (dry matter exclude fat). Hesperetin was the predominant flavonoid. The total phenolic content expressed as grams of gallic acid equivalents/100 grams fresh weight (excluding fat) was 2.0, 1.9 and 1.8 in F, DF and B samples, respectively. These results suggest that method of processing can significantly affect the content of flavonoids and their TAC values.