In this research, the antioxidant activity of extract from the leaves of Acacia confusa was evaluated by DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical and superoxide radical scavenging assays, lipid peroxidation assay, reducing power and metal chelating ability on ferrous ions assays, and trolox equivalent antioxidant capacity (TEAC) assay. Total phenolic contents and total flavonoid contents were also evaluated. In addition, column chromatography and high performance liquid chromatography are used to separate and purify the antioxidant compounds. The chemical structure of active constituents from A. confusa leaves was identified by the analysis of nuclear magnetic resonance spectroscopy, mass spectroscopy, IR spectroscopy and UV/VIS spectroscopy. Antioxidant results of methanolic extract from A. confusa leaves revealed that the crude extract, EtOAc soluble fraction and BuOH soluble fraction have great effectiveness in TEAC assay, and they also possess high amounts of total phenolic contents and total flavonoid contents, therefore these extracts exhibited great effectiveness in scavenging DPPH free radical, scavenging superoxide radical, inhibition of lipid peroxidation and reducing peroxidated substrates. Among those extracts, EtOAc soluble fraction possesses the highest amount of total phenolic content (281.0 mg of GAE/g) and total flavonoid content (108.0 mg of QE/g), and demonstrated the great capacity of scavenging DPPH free radical (EC50 = 7.0 μg/mL), inhibition of lipid peroxidation (EC50 = 110.0 μg/mL) and reducing peroxidated substrates. Moreover, the scavenging of superoxide radical of EtOAc soluble fraction (EC50 = 2.5 μg/mL) is more effective than catechin (EC50 = 7.0 μg/mL). EtOAc soluble fraction was then separated into 8 subfractions which were assayed by DPPH free radical and superoxide radical assays, reducing power and metal chelating on ferrous ions assays, and also determined their total phenolic contents and total flavonoid contents. Results revealed that subfractions Et6, Et7, and Et8 possessed the high amounts of total phenolic contentand total flavonoid content, they also exhibited the best antioxidant activities in DPPH free radical and superoxide radical scavenging assays. Ten compounds were isolated from EtOAc subfractions, including gallic acid gallate, luteolin, myricetin 3-O-(2’’-O-galloyl)-α-rhamnopyranoside 7-methyl ether, myricetin 3-O-(3’’-O-galloyl)-α-rhamnopyranoside, myricetin 3-O-(3’’-O-galloyl)-α- rhamnopyranoside 7-methyl ether, myricetin-3-glucopyranoside, myricetin-3- rhamnopyranoside, myricetin 3-O-(2’’-O-galloyl)-α-rhamnopyranoside, quercetin-3 -rhamnopyranoside and europetin-3-rhamnopyranoside. Among them, all compounds exhibited more effective capacity in scavenging DPPH free radical and TEAC than catechin except for luteolin and gallic acid methyl ether. In addition, the hot-water extract of A. confusa also have great effectiveness in DPPH and TEAC assays, and it possess high amounts of total phenolic contents (254.7 mg of GAE/g) and total flavonoid contents (35.8 mg of QE/g). Results obtained above indicated that the leaves of A. confusa have the potential to be used as a source for natural health products such as antioxidants.