Abstract: The convective heat transfer effect on the non-Newtonian nanofluid flow in the horizontal tube with Constant heat flux was investigated using computational fluid dynamics (CFD). For this purpose, non-Newtonian nanofluid containing Au and blood solution as a liquid with six particle concentrations of 1, 2, 4, 5 and 6 wt. % were used. Effect of particle concentration of Au-blood solution on convective heat transfer coefficient was investigated in different Reynolds numbers (4000 to 16000) for various tube diameters. The results showed that heat transfer coefficient and Nu number of non-Newtonian nanofluid increased with increasing concentration of Au Nano particles. By applying the modeling results, an equation was obtained for Nusselt number prediction using the dimensionless numbers.