[Objective] This study aims to enrich the experimental study of the ORC using mixture working fluids and analyze its transient and steady-state operating characteristics. [Methods] A 4-kW organic Rankine cycle(ORC) prototype using R236 fa/R123 was tested to obtain the transient and steady-state operating data. [Results] The results of the ORC system at different mixture concentrations reveal that the operation characteristics of the ORC with mixed working fluids are consistent with those using a pure working fluid. The adjustment of the working fluid mass flow rate significantly affects the system output power

while it has a limited impact on the thermal efficiency. The ORC system operates relatively stable with the variation in the mixture concentration

as it has a minimal effect on both the output power and thermal efficiency. With the increase in the R236 fa mass fraction

the expander inlet pressure is stable while its outlet pressure gradually increases

resulting in high pressure ratios. This phenomenon indicates that adopting the expander with a larger internal volume ratio can optimize the ORC performance. The trade-off between the exergy destructions of the evaporator and condenser at different mixture concentrations is the main factor determining the system performance. The temperature glide caused by the condenser pressure drop limits the attribution of the mixture working fluid to optimize the system performance. [Conclusions] In the design and operation of mixed-working-fluid ORC systems

it is crucial to consider the matching of the condenser pressure drop and the working fluid inherent properties.