Statistical experimental designs were applied for the optimization of phytase production by a marine yeast Kodamaea ohnieri BG3 in a cost-effective oats medium. Using Plackett-Burman design, oats, ammonium sulfate and initial pH were identified as significant factors and these factors were subsequently optimized using a central composite design (CCD). The optimum variables that supported maximum enzyme activity were oats 1.0%, ammonium sulfate 2.3%, glucose 2.0%, NaCl 2.0% and initial pH 6.3. The validity of the optimized variables was verified in shake-flasks level. An overall 9-fold enhancement in phytase activity (62.0 -> 575.5 U/ml) was attained due to the optimization. (c) 2007 Elsevier Ltd. All rights reserved.