Continuous hydrolysis of chitosan was performed in a convoluted fibrous bed bioreactor (CFBB) with immobilized T. reesei. At dilution rate of 0.4d(-1) and substrate concentration of 2%(mass vs. volume), the average degree of polymerization of hydrolysate can be kept at 1.25-1.35, which can be easily regulated by changing dilution rate or inlet chitosan concentration.