PROBLEM TO BE SOLVED: To provide a novel amino polysaccharide which has a similar structure to conventional chitosan, while has a high solubility and a low viscosity to water and the like, as well as is easy to handle and has various applications.SOLUTION: Provided is an amino polysaccharide having a structure bound in a structure formed by alternately linking glucosamine by &bgr;1 → 3 binding and &bgr;1 → 4 binding. The amino polysaccharide having a molecular weight of 300,000-500,000 produced by Molecular Peyronellaea calorpreferens NITE P-01575 strain or a natural or artificial variant thereof is available as a waste fluid purification agent for purifying waste fluid by coagulation-sedimentation method.【課題】従来のキトサンと類似した構造を有するが、水等への溶解性が高く粘性も低く、取り扱いが容易で多様な用途を有する新規アミノ多糖を提供する。【解決手段】グルコサミンがβ1→3結合とβ1→4結合で交互に連なる構造で結合した構造を有するアミノ多糖を提供する。分子ペイロネラ カロプレフェレンスNITE P-01575菌株或いはその自然的或いは人工的変異体の産生した分子量が300,000~500,000であるアミノ多糖。凝集沈殿法により廃液の浄化を行う廃液浄化剤として、利用可能である。【選択図】なし