Optical fiber coatings play an important role in fiber strength, fatigue, and attenuation. Polyimide coatings on optical fiber are in growing demand because of their excellent high-temperature properties. Mechanical and optical characterizations of polymide-coated optical fibers were carried out at different temperatures. The strength was virtually unchanged at room temperature and at 300°C in air. Fatigue parameters (n values) were greater than 30 when tested in water at 80°C. Optical attenuation was unchanged when the fibers were tested at 340°C for 48 h. When the fibers were subjected to — 40°C to +70°C temperature cycling, the change in attenuation was less than 0.1 dB/km at 850 nm.