A novel polysaccharide derivative, a drug carrier comprising a novel polysaccharide derivative, and a drug complex are disclosed. The polysaccharide derivative according to the present invention comprises a polysaccharide having a carboxyl group in which a peptide chain is introduced at a part or all of the carboxyl groups of the polysaccharide. The peptide chain comprises 1-8 amino acids which may be the same or different. A part or all of the amino groups in the peptide chain which are not involved in the linkages with the carboxyl groups of the polysaccharide or the carboxyl groups in the peptide chain may form an acid amide linkage or an ester linkage with a carboxyl group, an amino group or a hydroxyl group of a third compound such as drugs. The polysaccharide derivative has a property of accumulating in a high amount at a tumor, and thus can deliver efficiently a drug which has a side-effect or a limited sustainment of the drug efficacy to the tumor.