The purpose of this investigation is to make clear fundamental characteristics of convension performance of kinetic energy of a two-phase flow into work. As the first step, and experimental study of power generation by a Pelton-type turbine was conducted using an air-water two-phase mixture as the working fluid. The characteristics of the output and the efficiency for air and water flow rates were investigated. The efficiency was expressed as a function of the void fraction α and the flow pattern as follows : α<0.84 (bubbly flow) : η_max=0.75-0.20α α>0.84 (annular-mist flow) : η_max=2.5-2.3α The water flow rate ranged from 0.167 to 2.2 kg/s, the air flow rate from 0 to 17×10^-3 kg/s, and the output frm 0 to 280 W.