The crystallization properties of ZrF4-based fluoride glasses containing PbF2 are clarified and single-mode fibers for an optical amplifier operating at 1.3 μm are fabricated. The crystallization tendency increases as the PbF2 content of the glasses increases and the optimum PbF2 content ranges from 11 to 12.5 mol % in terms of glass stability and refractive indices. The 4%-Δn single-mode fiber with a transmission loss of 44 dB/km at 1.2 μm was prepared as the amplifier host fiber. ZrF4-based glass with a PbF2 content of 11 mol % was used as a core glass and HfF4-based glass was used as a cladding glass.