An experimental study is conducted to investigate the effects of inclination angle on the natural convection of nanofluids inside a cubic cavity with the side size of 10 cm. One of the surfaces of the cavity is kept in cold temperature and another one (opposite side) in hot temperature while the other four surfaces are insulated. The mixtures of three different types of nanoparticles including Al2O3, TiO2, and CuO within turbine oil (TO) are used as the heat transfer fluid. The heat transfer in the cavity is investigated in three inclination angles with respect to the horizontal position including 0 degrees, 45 degrees and 90 degrees where the weight fractions of nanoparticles are 0.2%, 0.5%, and 0.8%. The Nusselt number results are presented for the three types of nanofluids, and different angles of inclination, Rayleigh number, and weight fraction of nanopartides. The results reveal that the turbine oil has the highest Nusselt number in any inclination angle of the cavity compared to the nanofluids. Also, it is found that at the inclination angle of 90 degrees and the weight fraction 0.2%, the application of TiO2 particles results in the maximum Nusselt number while for weight fraction of 0.8%, the maximum Nusselt number is associated with the CuO nanopowders. (C) 2014 Elsevier Ltd. All rights reserved.