Turbulent flow of inelastic non-Newtonian fluids in horizontal tubes was investigated. The flow region has been classified into two regions, namely, the entrance region in which the velocity and temperature profiles begin to take form, and the fully developed region in which the shape of the profiles are self-preserving. In the entrance region, both heating effect and cold flow (isothermal)cases were considered. As such, two models are proposed for prediction of the hydrodynamic and thermal entrance lengths. It was found that non-Newtonian fluids have longer hydrodynamic and thermal entrance lengths than the Newtonian fluids. The models were only compared to the experimental data for Newtonian fluids because there is no published experimental data of non-Newtonian fluids. In the fully developed region, it has been assumed that the flow region could be separated into two zones, namely, the viscous sublayer, and the outer regions. The model was tested for its validity with the experimental data. The new correlation which covers a broader range of flow behavior indices and Reynolds numbers accurately predicts the heat transfer to both transitional and turbulent flow regimes and offers the advantage of simplicity and accuracy based on the absolute percent arithmetic average deviation and percent standard deviation.