In this paper, the efficiency of an evacuated U-tube solar collector (EUSC) with ZnO/Etylene Glycol-Pure Water (ZnO/EG-PW) as a working fluid was experimentally investigated. 50%-50% EG-PW was used as a base fluid. To prepare the nanofluids ZnO nanoparticles were added to the EG-PW base fluid at different volume concentrations (1.0%, 2.0%, 3.0% and 4.0%). The maximum collector efficiency was obtained at equal working fluid inlet temperature and ambient temperature in all experiments. Moreover, the highest collector efficiency was determined 62.87% for 3.0 vol.% and mass flow rate of 0.045 kg/s that it was 26.42% higher than EG-PW as a working fluid. Also, this value is 5.2% and 6.88% higher than the base fluid for the mass flow rates of 0.03 and 0.02 kg/s, respectively. It was determined also that the thermal conductivity of ZnO/EG-PW nanofluid increases with increasing nanoparticle volume concentration. (C) 2018 Elsevier Ltd. All rights reserved.