the invention relates to a method for the production of xylitol , the method comprising providing a microorganism having xylanolytic activity , and a microorganism capable of converting a pentose sugar to xylitol ; or providing a microorganism having xylanolytic activity and being capable of converting a pentose sugar to xylitol , culturing the microorganism of step or the microorganism of step in a medium comprising polymer or oligomer materials containing pentose sugars in conditions sufficient for enabling hydrolysis of said polymers or oligomers by the microorganism ; producing xylitol in the microorganism of step or in the microorganism of step by bioconversion of the hydrolysis products obtained in step , and recovering said xylitol produced . the invention also relates to a microorganism , which has xylanolytic activity and has been genetically modified to enhance its xylanolytic activity , and to reduce its xylitol metabolism .