PROBLEM TO BE SOLVED: To provide cellulose-derived materials that resist viscosity reduction even when subjected to high temperatures.SOLUTION: A carboxymethylated cellulose fiber has an average fiber diameter of 3-500 nm, preferably 3-20 nm, an aspect ratio of 100 or more, and a carboxymethyl substitution degree of 0.01-0.30 per glucose unit.SELECTED DRAWING: None【課題】高温にさらしても減粘しにくいセルロース由来の材料の提供。【解決手段】平均繊維径が３～５００ｎｍ、好ましくは３～２０ｎｍ、アスペクト比が１００以上、グルコース単位当たりのカルボキシメチル置換度が０．０１～０．３０である、カルボキシメチル化セルロース繊維。【選択図】なし
