The performance of a small organic Rankine cycle (ORC) power system with a radial turbine as its expander and R123 as the working fluid was experimentally investigated based on 90 ℃ low-temperature waste heat sources. With maximum power output by unit hot water as target function, the ORC various operation conditions were studied in experiment. The results indicate that the critical pressure ratio of R123 is at the range of 0.59-0.67, which increases slightly with the increase of the working fluid pressure, and a converging-diverging nozzle is needed for experimental system. The maximum power output is synthetically affected by heat transfer performance, turbine efficiency, drive-power generation efficiency, total power and other factors of the system. The optimum evaporation pressure and the corresponding maximum power output per unit mass of heat source water is 0.46 MPa and 0.40 kJ/kg, respectively; while the optimum condensation pressure and the corresponding maximum power output are 0.11 MPa and 0.76 kJ/kg, respectively. ©, 2015, Science Press. All right reserved.