PURPOSE: To provide a polyester fiber having improved raising easiness and color-developing property by forming specific fine pores to an ultra-fine fiber and to provide a process for the production of the polyester fiber.

CONSTITUTION: The objective polyester fiber is produced by forming a specific number of fine recesses having a width corresponding to 5-50% of the fiber diameter on the surface of a polyester fiber having a thickness of ≤0.5de. It can be produced by producing a fibrillatable conjugate fiber by using a polyester component containing inert inorganic fine particles having a specific particle diameter, fibrillating the conjugate fiber and thinning the product at a thinning ratio of ≥10wt.%. A cloth made of the fiber can extremely easily be raised without damaging the cloth and gives excellent color-developability when dyed with a dye.