An optical fiber operating in the mid-infrared wavelength range is fabricated using ZrF4-based fluoride glass. Material purification, the fiber fabrication process, and transmission properties are presented. The starting materials, ZrF4, BaF2, GdF3, AlF3, and SbF3are carefully purified by sublimation techniques. The "built-in" casting technique, specially developed for fluoride glass fiber, is used for preparing cladded type fiber with a smooth core-cladding interface. Spectral loss is measured in the 0.7- to 5.5-μm wavelength region, and a minimum loss of 12 dB/km is attained at 2.55 μm. Based on the refractive-index spectrum measured in the m range, material dispersion characteristics are also investigated. It is indicated that material dispersion falls to zero at 1.52 μm and exhibits a gentle wavelength dependence in the present glass system.