PET/germanium composite fibers that with negative air ion release and far infrared emission properties were prepared by adding germanium particles to polyethylene terephthalate (PET) and melt-spinning. The morphology, effect of the germanium content on the negative air ion release, far infrared emission, thermal and mechanical properties of the fibers were investigated. The germanium particles uniformly disperse in the PET fibers when the concentration ranged from 1% to 3 percent. The value of the negative air ions released by the PET/germanium composite fibers increased with increasing content of germanium and reached 1470 ions/cm-3 at 3% germanium concentration. The highest far infrared normal emissivity (0.9) was obtained at 3% germanium concentration. The TG and DSC analysis revealed that the two heat histories used had little effect on the PET. The crystallinity of the composite fibers decreased with increasing germanium content. Water fastness testing showed that the PET/germanium composite fibers had excellent and durable negative air ion release and far infrared emission properties. The breaking strength of the fibers decreased with increasing of the germanium content.