The glass system consisting of ZrF4, BaF2, LaF3, NaF, and AlF3has been developed for optical fibers operating in the mid-infrared region. The glasses in the system possess less tendency to crystallize and favorable optical properties. Additives to improve light scattering characteristics of the fluoride glasses are reported. Rayleigh scattering in the fluorozirconate glass has been ascertained to be as low as in synthetic silica glass. The theoretical transmission losses for the fluoride glass fibers are estimated to be 0.001 dB/km at 3.2 μm and 0.005 dB/km at 3.5μm oxygen reduction in fluoride glasses, which is one of approaches to achieve such a low-loss fiber, is discussed.