Response surface methodology (RSM) was used to optimize the extraction parameters for Pholiota adiposa SX-02 intracellular polysaccharide (IPS) produced during submerged culture. The optimum conditions of IPS extraction were predicted to be, ultrasonic power at 564.93W, precipitation time 30.34 h and pH 8.28, and IPS yield was estimated at 19.75%. The actual value of IPS under these conditions was 20.51%. The in vitro antioxidant results showed that the inhibition effects of IPS at a dosage of 250 mg/l on superoxide anion, hydroxyl and 1,1-dipheny1-2-picrylhydrazyl (DPPH) radical were 74.66 +/- 5.31%, 69.20 +/- 5.13%, and 75.20 +/- 6.73%, respectively, which were 27.51 +/- 2.23%, 16.58 +/- 1.33%, and 9.46 +/- 0.72% higher than that of butylated hydroxytoluene (BHT), respectively. The reducing power of IPS was 0.32 +/- 0.02 (absorbance at 700 nm), 39.13 +/- 3.47% higher than that of BHT. The results provide a reference for large-scale extraction of IPS by P. adiposa SX-02 in industrial fermentation and the IPS can be used as a potential antioxidant which enhances adaptive immune responses. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.