Abstract: In a flame-retardant coated optical fiber, which comprises an optical fiber, a primary coating layer covering the optical fiber, and a secondary coating layer covering the primary coating layer, the primary coating layer is made of an ultraviolet-curing resin, and the secondary coating layer is made of a resin composition containing 20 to 70 parts by weight of ethylene-bis-tetrabromophthalimide and 5 to 40 parts by weight of antimony trioxide, based on 100 parts by weight of thermoplastic polyester elastomer. The secondary coating layer of the coated optical fiber has high flame retardancy which is in conformity to the UL standard, and the bonding strength between the primary and secondary coating layers is high enough. Thus, a projection of the optical fiber during actual use is too small to damage a light source.