The performance of a new zeotropic mixture of R245fa 60%/R134a 40% (molar concentration) in small scale ORC (organic Rankine cycle) was proposed and evaluated experimentally. For a range of heat source temperatures, the power output and thermal efficiency of the ORC system with this mixture was analyzed. The experimental data is presented for a 1 kW scroll expander and a heat source temperature between 80 and 120 degrees C. The results showed that the proposed zeotropic mixture increases the power output compared to an identical ORC with pure R245fa despite working at a lower pressure ratio. With increasing heat source temperature, the pure R245fa ORC becomes increasingly vigorous. Therefore, the best application of this mixture would be in heat sources with temperatures between 80 degrees C and 100 degrees C, where the pure R245fa ORC cannot have a high expander inlet pressure; hence, it works at lower pressure ratios. (C) 2015 Elsevier Ltd. All rights reserved.