This paper presents a numerical study of entropy generation and mixed convection heat transfer of Cu-water nanofluid flow in an inclined open cavity uniformly heated from the left wall. The governing equations, which are continuity, momentum and energy equations, are solved using a finite volume method. The investigation is carried out in the range of the inclination angle of the cavity 0 degrees <= 6 gamma 6 <= 360 degrees and the range of nanoparticle volume fractions 0 <= phi <= 0.06, for three Reynolds numbers Re = 100, 300 and 500 while fixing the Grashof number at Gr = 10(4). Results show that the flow field, the temperature distribution, the heat transfer mode, the heat transfer and the entropy generation rates, and the magnitude of irreversibilities in the entropy generation are strongly affected by the inclination angle. This depends on the Reynolds number and the volume fraction of nanoparticles. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.