An optical fiber operating in the mid-infrared wavelength range is fabricated using ZrF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> -based fluoride glass. Material purification, the fiber fabrication process, and transmission properties are presented. The starting materials, ZrF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> , BaF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , GdF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , AlF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> , and SbF <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> are 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4-5-\mu</tex> 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.