PROBLEM TO BE SOLVED: To provide a modification method of cellulose capable of reducing the granulocyte activating function of cellulose. SOLUTION: This modification method of cellulose for remarkably reducing the granulocyte activating function of the original cellulose in contacting with blood, comprises fixing a compound having log P (P is a distribution coefficient in octanol-water system) value of >=2.30 on the cellulose.