The effect of thermal stresses on the static fatigue of double-coated optical fibers is investigated. The thermally induced tensile stresses on the glass fiber in double-coated optical fibers in the long term are derived by the viscoelastic theory. The lifetime of the glass fibers is dominated by the tensile stress on the glass fibers, which is a function of material's properties of the polymeric coating and its thickness. To minimize these thermal stresses in the long term, the radius, Young's modulus, the thermal expansion coefficient and the relaxation time of the polymeric coating should be decreased. Additionally, based on strength consideration, the radius and Young's modulus of the polymeric coating should be thick or hard enough to support the external mechanical stresses. (C) 2004 Elsevier B.V. All rights reserved.