Large capacity oil-free screw compressors are mainly used in petrochemical plants such as styrenemonomer, and linear alkyl benzene plants, where suction and discharge pressures are relatively low and large capacity is needed. Recently, these plants have tended to become larger and the requested capacity to the compressor also has tended to become larger. To satisfy such a market needs, we have developed the world's largest capacity oil-free screw compressor "Model KS80" by using the design technology and manufacturing technique of the large screw compressor. In this paper, the design concepts and features of "Model KS80" are introduced.