Aspartic acid as a hydrophilic group is added to the main structure of multi-walled carbon nanotubes (MWNT) for synthesizing highly-dispersed MWNT-based water nanofluids with different concentrations. Chemical treatment is analyzed and functionalization is confirmed by TGA, FTIR, Raman spectroscopes. The present study is followed by investigation of thermo-physical properties as well as heat transfer rate of circular tube at constant heat flux in the presence of non-covalently and covalently-functionalized MWNT with aspartic acid. The prepared nanofluids in three weight concentrations of 0.05%, 0.1% and 0.2% are investigated in the flow rate range of 2.86-8.85 ml/s. Thermophysical properties, convective heat transfer coefficient, pressure drop, friction factor, performance index and pumping power results suggest that functionalized MWNT with aspartic acid is one of the most appropriate alternative coolant for water in industry. (C) 2015 Elsevier Ltd. All rights reserved.