application/pdf Improvement of the generation power in micro-hydraulic turbines is shown in the range of low flow rate and low head using a new inverter generation system. The generation power can be obtained down to very low flow rate and head using the new inverter generation system with variable rotational speed control, where a water turbine connot produce the electric power in a normal constant-speed-control system. Experiments were carried out using a practical micro-hydraulic turbine with 2 kW output and variable rotational speed in a forest on the mountain, Mie University. The total efficiency is kept at a high value even in the very low partial load area. Compared with the constant speed control, the generation power is improved over 20 percent by varying the rotational speed.