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The yield, composition, structure and biofunction of microorganism exopolysaccharide (EPS) depended on their genetics and metabolic pathways. An EPS-producing endophytic fungus was isolated from Angelica sinensis planted in Dingxi, Gansu, China, and identified as Alternaria tenuissima F1. The production optimization, purification and characterization of the purified EPS from A. tenuissima F1 and the in-vitro antioxidant potentials was investigated. Results showed the optimal medium composition were 8% mannose, 2% yeast extract, 0.04% MgSO 4 ·7H 2 O, 0.005% Vc, and the optimal cultivation conditions were set at initial pH 7.0, culture temperature 30 °C, inoculum size of 3%, 180 r/min for 5 d. The EPS purified by ion exchange column chromatography and gel chromatography was a non-reducing sugar and glycoprotein with pyranoid ring by Fourier transform infrared spectroscopy (FT-IR) analysis, displayed a porous network structure by scanning electron microscope (SEM) observation and exhibited a high thermal stability with the degradation temperature of 303.9 °C by thermogravimetric analysis (TG/DSC). Molecular weight of the purified EPS was 3.246 × 104 g/mol, and EPS was composed of d -galacturonic acid, rhamnose, d -mannose, glucose, and d -galactose in ratio of 0.45:3.02:3.25:1.0:0.95. The EPS exhibited strong scavenging activity and may be a new source of natural antioxidant. Unlabelled Image • EPS from A. sinensis endophytic fungus A. tenuissima F1 were optimized by orthogonal experiment and response surface methodology. • The purified EPS showed some different physicochemical properties. EPS has a strong antioxidant activities. [ABSTRACT FROM AUTHOR]