PURPOSE: To produce an antistatic polyester fiber having high operation stability and quality stability and keeping high antistaticity having excellent washing fastness even after a severe alkali-thinning treatment.

CONSTITUTION: A polyester fiber containing 0.5-2wt.% of a polyoxyalkylene glycol or its derivative and 0.1-1wt.% of an organic metal salt in a polyester matrix is incorporated with 0.1-3wt.% of a polysiloxane having a viscosity of >10,000 cst at 25°C. The polyoxyalkylene glycol or its derivative is dispersed as independent island components in the arbitrary cross-section of the fiber and the size of the largest island component is 0.1-0.5μm.