Anofluids are suspensions of metallic or nonmetallic nanopowders in base liquid and can be employed to increase heat transfer rate in various applications. In this work turbulent flow forced convection heat transfer of Al2O3-water nanofluid inside an annular tube with variable wall temperature was investigated experimentally. The Nusselt number of nanofluid was obtained for various Reynolds numbers and nanoparticle concentrations at atmospheric pressure. The addition of nanoparticles in water enhances heat transfer coefficient and the enhancement increases with increase in the nanoparticle concentration and flow rate. Experimental results emphasize the enhancement of heat transfer due to nanoparticles presence in the fluid.