PURPOSE: A mixture of linea aromatic polyester and a specific organic compound is, after formed, treated with an alkali and beaten to produce said pump having extremely fine and uniform fibri structure and giving paper with high strength and good printability.

CONSTITUTION: A mixture of (A) linear aromatic polyester, preferably consisting mainly of the recurring units of the formula (n=2W6) and (B) an organic compound that is incompatible with component A and soluble in an alkaline solution is formed into fiber or hollow fiber preferably. The formed product is treated with an alkaline solution, preferably aqueous sodium hydroxide or potassium hydroxide and beaten. Component B has preferably 2 or more difference in solubility parameter from component A and an organic sulfonate metal salt is preferred. The amount of component B is preferably 1W10wt%.