The effects of annealing on the properties of hermetically carbon-coated optical fibers are investigated. The hermetically carbon-coated optical fibers are prepared by the plasma enhanced chemical vapor deposition method using methane and hydrogen as the precursor gases. The annealing temperatures are selected at 100, 200, 300, 400, and 500°C, respectively. The thickness, optical band gap, and microstructure of carbon films are measured. Meanwhile, the water-repellency and low-temperature surface morphology of carbon-coated optical fibers are evaluated. The results indicate that the thickness and defect content of the carbon films decrease with increasing the annealing temperature, while the degree of structure order and the amount of microcrystalline graphite in the carbon films increase. When the annealing temperature is over 300°C, the carbon films acquire enough thermal energy to cause a great amount of hydrogen and hydrocarbon to be released, and the carbon films transform to the graphitelike structure. Additionally, based on the evaluation of water-repellency and low temperature–induced break or delamination of carbon films, it is found that the carbon film annealed at 300°C is the best one for use as the hermetic optical fiber coating.