Power transmitting capabilities of polycrystalline (PC) KRS-5 fibers have remarkably increased since the first report by researchers at Hughes Research Laboratories. Maximally transmitted power of CW CO2 laser beam through PC KRS-5 fiber has reached up to about 100W. The power density at the fiber input end is 36 KW/cm2 and remarkable damage is not observed. Mechanical properties of PC KRS-5 fiber is superior to any other PC fiber, therefore PC KRS-5 fiber is a hopeful waveguide for the practical use of CO2 laser power transmission. And also it is applicable for IR sensor systems in a short range. When the power transmission capabilities of PC KRS-5 fiber will be attained up to several hundreds watt, it will be widely used in the field of the CO2 laser machining.