Inulooligosaccharide (IOS) production from pure inulin was carried out using a dual endoinulinase system originated from Xanthomonas sp. and Pseudomonas sp. A statistical experimental design was employed to obtain the best possible combination of pH, temperature, enzyme dosage ratio and substrate concentration for maximum inulooligosaccharide production based on the initial reaction rate of the dual enzyme system. The optimum reaction conditions were as follows: pH, 5.8; temperature, 50 degreesC; substrate concentration, 50 g/liter. The maximum conversion yield was 92% when 50 g/liter of pure inulin was incubated with the dual enzyme system containing Xanthomonas enzyme to Pseudomonas enzyme in the ratio of 4:1 for 110 h. Substrate inhibition was not detected for a prolonged reaction period of 110 h up to 150 g/liter of inulin with an enzyme dosage of 460 U/g substrate. By use of the dual enzyme system, higher conversion yield of IOS and even product composition were achieved.