Six factors: strain, carbon source, nitrogen source, nitrogen concentration, aeration, and initial pH, were investigated for their effects on exopolysaccharides (EPS) production in Erlenmeyer flasks by Aureobasidium pullulans using 2-level fractional factorial design. The concentration and molecular weight (MW) of EPS were optimized simultaneously. The effects of main factors together with possible two-factor interactions were detected, and the levels of the six factors were optimized using empirical models. Analysis of factor effects revealed that strain had the strongest influence on EPS concentration, and nitrogen source on MW of EPS. However, nitrogen concentration did not show significant influence on both parameters. The influences of factors on the production variability were also monitored for quality control purposes. At the optimum levels of control factors investigated, as high as 22.6 g/L EPS with a weight average MW of higher than 2 x 10(6) was produced. The results of this work indicate that the production kinetics varies for different microorganism-medium-environment systems. (C) 2007 Elsevier Ltd. All rights reserved.