When the ether-based cellulose derivative (A), the polymer (B) different from the ether-based cellulose derivative, and the alcohol-based solvent (C) are mixed, a solution phase containing the ether-based cellulose derivative (A) as a main component； The emulsion is formed in a system in which the two phases of the solution phase containing the polymer (B) as a main component are phase-separated and the solvent of each phase separated into the two phases is substantially the same. And a poor solvent (D) are contacted to obtain ether-based cellulose derivative fine particles having an average particle diameter of 1-1000 μm, linseed oil absorption of 50-1000 mL / 100 g, and an average surface pore diameter of 0.05-5 μm.エーテル系セルロース誘導体（Ａ）と、エーテル系セルロース誘導体とは異なるポリマー（Ｂ）と、アルコール系溶媒（Ｃ）とを混合したときに、エーテル系セルロース誘導体（Ａ）を主成分とする溶液相と、ポリマー（Ｂ）を主成分とする溶液相の２相に相分離し、前記２相に相分離した各相の溶媒が実質的に同じになる系において、エマルションを形成させた後、前記エマルションと貧溶媒（Ｄ）を接触させることで、平均粒子径が１～１０００μｍ、アマニ油吸油量が５０～１０００ｍＬ／１００ｇ、平均表面細孔径が０．０５～５μｍのエーテル系セルロース誘導体微粒子を得る。
