In this study, the liquid culture conditions were optimized for maximal production of mycelial biomass and exopolysaccharide by Paecilomyces japonica. The effects of medium composition, C/N ratio and physical parameters were investigated. From these experiments, 30 g glucose, 20 g yeast extract, 0.5 g KH2PO4, and 0.1 g CuCl2 2H(2)O in 1-l distilled water were found to be the most suitable carbon, nitrogen, and mineral sources, respectively. The optimal temperature, initial pH, agitation, and aeration were determined to be 27 degrees C, uncontrolled pH, 400 rpm, and 1.0 vvm, respectively. Under these optimal conditions, the maximum mycelial growth and polysaccharides production were 23.1 g/l and 2.5 g/l, respectively. (C) 2012, The Society for Biotechnology, japan. All rights reserved.