Abstract: Obesity is the major factor inducing high blood lipid，fatty liver，diabetes，cardiovascular disease and so on. And it has become one of the important problems harming the health of people worldwide. In order to obtain a new low density lipoproteins (LDL) adsorbent，chitosan (CTS)，which is polycationic，was modified to prepare a polyanionic derivative. In this paper，based on Mannich reaction，a novel polyanionic chitosan derivative—N-methylene chitosan phosphate ester (NMCP)，was synthesized by introducing the phosphorous acid into the amido group of chitosan. The chemical structure and properties of NMCP was characterized with FT-IR，XRD and dynamic contact angle meter. The absorbability of CTS and NMCP with respect to lipoprotein was also studied.