Abstract: The polyethylene naphthalate fiber for industrial material having a low fatigue in a composite is a polyethylene naphthalate fiber for industrial material containing an ethylene-2,6-naphthalate unit in 80% or more, characterize by having a strength of 6 cN/dtex or more and a secondary yield point elongation degree of 8% or less. The production method thereof is a method for producing a fiber in which a fiber having been obtained by melt-spinning a polyethylene naphthalate is subjected to stretching, characterized in that prestretch satisfying such conditions as the fiber temperature of from 80° C. to 120° C. and from 0.05 to 0.3 N/dtex is performed, a first stretch satisfying such conditions as the fiber temperature of from 130° C. to 180° C. and stretch tensile force of not more than the prestretch tensile force is performed, the total stretch magnification including subsequent stretches is set to 5 or more, and finally heat-treatment under tension with a stretch ratio of from 0 to 2% is performed.