A rapid compression-expansion machine was developed, which can simulate intake, compression, expansion and exhaust strokes in a single Diesel cycle by an electrically controlled and hydraulically actuated driving system. The whole system which is composed of a hydraulic actuator, fuel injector and a valve driving device, is sequentially controlled by a micro-computer. The machine features; 1) accurate control of piston position at TDC, 2) no effect of lubricant on HC emission due to the use of dry piston rings; 3) independent control of local wall temperature; and 4) high power output to drive heavy piston at high frequency. The single cycle operation permits Diesel combustion experiments under a wide range of operating conditions and easy access of optical diagnostics with minimized amount of test fuel. The performance test showed that the machine can drive a DI Diesel type piston with a 100 mm bore at a maximum frequency of 16.7 Hz at a maximum compression pressure of 15 MPa.MODERN DIESEL ENGINES demand higher supercharging, exhaust gas recirculation ( EGR ), higher temperature of combustion chamber surfaces and the use of various kinds of fuels. In experiments of these subjects using practical engines, durability and optical access for the observation of the combustion phenomena is demanded for test engines. But it is generally difficult to realize these. Therefore, a rapid compression machine or rapid compression-expansion machine which can achieve a single cycle combustion experiment has been used efficiently for specific purposes(1, 2, 3 and 4). The authors developed a rapid compression-expansion machine provided with an electrically controlled and hydraulically actuated driving system, and have conducted various experiments. The experiments showed that this machine has the following features; 1) local wall temperatures of the combustion chamber can be controlled independently, 2) emission test without the effect of lubricating oil is possible by the use of oilless piston rings, 3) the in-cylinder gas condition at TDC can be changed widely by changing temperature, pressure, density and gas composition in the gas reservoir which is connected to the intake port, 4) only a small amount fuel is consumed, 5) various optical diagnostics can be easily accessed.Based on the experience in operating the first rapid compression-expansion machine, the authors developed recently a new rapid compression-expansion machine which has more power, longer stroke and an improved hydraulic-mechanical oil brake system. A performance test showed that this machine can operate at a maximum cylinder pressure of 15 MPa, which is expected in future high supercharged Diesel engines. This paper will describe the design and the performance of the new rapid compression-expansion machine.