To provide a fine cellulose ester fiber having high heat-resistance and improved adhesiveness to a resin.

Natural cellulose is made to react with an N-oxyl compound as an acid catalyst and a cooxidation agent. The reaction product fiber is dispersed in a solvent, treated with an organic onium compound and esterified by reacting with an alkylation agent to obtain the fine cellulose ester fiber containing an esterified uronic acid residue in the molecule and having a cellulose I crystal structure.