PURPOSE: To obtain polyester fibers having unique surface conditions shapes and improved coloring properties, by dissolving the surface of polyester fibers containing fine inert inorganic particles of specific particle diameter with a solvent having solubility or decomposing ability.

CONSTITUTION: Polyester fibers containing 0.12W0.50wt%, preferably 0.3W 0.48wt%, inert fine inorganic particles having an average particle diameter ≤100 millimicrons, preferably ≤20 millimicrons, are treated with a solvent having the solubility or decomposing ability for the fibers, preferably a solution of caustic soda, to dissolve the surface thereof and give the aimed fibers. Silica is preferred as the inert inorganic fine particles, and a hydrophobic dry silica, having alkyl groups at the surface thereof, and silanol groups sealed on the particle surface, prepared by the dry method is more preferred.