Optimization of the growth conditions for maximum P-mannanase production in shake flasks by using recombinant Aspergillus sojae ATCC11906 (AsT1) was carried out by Box-Behnken design of response surface methodology. The highest beta-mannanase activity on the fourth day of cultivation at 30 degrees C was obtained as 363 U/ml in the optimized medium consisting of 7% sugar beet molasses, 0.43% NH(4)NO(3), 0.1% K(2)HPO(4) and 0.05% MgSO(4) (by weight per volume) at 207 rpm. On the sixth day of cultivation under the optimized conditions, the highest beta-mannanase activity was achieved as 482 U/ml which is 1.4-fold of 352 U/ml activity found on glucose medium previously. (C) 2010 Elsevier BM. All rights reserved.