Chitosan was linked to invertase by covalent conjugation to periodate-activated carbohydrate moieties of the enzyme. The thermostability of modified enzyme was enhanced by about 10 degrees C. The half-life at 65 degrees C was increased from 5 min to 5 h. The enzyme stability was enhanced by 20% at pH below 3.0. The half-life of denaturation by 6 M urea was increased by 2 h.