Single-mode optical fibers are obtained using ZrF4-based fluoride glasses. The fibers are drawn from a preform and jacketing tube. The preform with cladding/core ratio of 5.1 is made by using a built-in casting method. The cutoff wavelength of the fiber is experimentally determined to be 2.7 μm by bending loss measurement. Minimum transmission loss of the obtained fiber is 160 dB/km at a wavelength of 3.28 μm. The -value at this wavelength is estimated to be 2.03 from the core diameter and the refractive index difference.