Technical trend of refrigeration system using natural refrigerants (or natural working fluids) was generally overviewed mainly by the proceedings of the International Conference of Natural Working Fluids past these few years. Hydrocarbon, carbon dioxide, water and air are mainly used as new refrigerants. Risk assessment of these flammable refrigerants was widely discussed. Hydrocarbon has been already widely used for refrigerators in Germany. Carbon-dioxide is now focused as a new refrigerant for air-conditioners of automobiles and water heaters. Turbo chiller with water as refrigerant has been tested in Germany. Air cycle refrigeration systems were applied to commercial freezer and for transportation. Natural refrigerants are also paid attention as secondary refrigerants.