Higher efficiencies and optimal utilization of geothermal energy require a careful analysis of Organic Rankine Cycle (ORC) which is suitable for converting electric power from low-temperature heat sources. The objective of this study is to experimentally analyze the effect of varying working fluid mass flow rate and the regenerator on the efficiency of the regenerative ORC operating on R123. As R123 presents a low boiling point temperature (27.82 degrees C), a technology was invented to address the leakage issue when transferring R123 between the inside and outside of the regenerative ORC system. A specially manufactured throttle valve was adopted in the bypass subsystem to protect the turbine during the starting and closing processes and a novel phenomenon was discovered during the test. A preliminary test of the system was conducted with a geothermal source temperature of 130 degrees C. The experimental results show that the power output is 6 kW and the regenerative ORC efficiency is 7.98%, which is higher than that of the basic ORC by 1.83%. (C) 2013 Elsevier Ltd. All rights reserved.