Experimental study of nanofluid flow and heat transfer to fully developed turbulent forced convection flow in a uniformly heated tubular horizontal backward-facing step has reported in the present study. To study the forced convective heat transfer coefficient in the turbulent regime, an experimental study is performed at a different weight concentration of Al O nanoparticles. The experiment had conducted for water and 2 3 Al O-water nanofluid for the concentration range of 0 to 0.1 wt.% and Reynolds number 2 3 of 4000 to 16000. The average heat transfer coefficient ratio increases significantly as Reynolds number increasing, increased from 9.