The effect of temperature-dependent viscosity on the flow development behavior inside a circular pipe was studied. The development of centerline axial velocity is presented at different axial positions throughout the tail straight pipe of test section by measurements carried out experimentally using Pitot tube and computed numerically using ANSYS FLUENT 16 software code. The measurements were conducted for various flow rates depending on the control valve opening at two different temperature of fluid 30°c and 60°c. It was found that the computational results showed a good trend agreement with the experimental results. The influence of heat on the density and viscosity of fluid leads to increasing flow rate and Reynolds number. Therefore, it was observed that the hydrodynamic entrance length has been increased due to heating the fluid. The length was increased by 21.4% for the lower flow rate, which is more than the percentage obtained for the higher flow rate. The results also show that the values of centerline velocity for a fully developed region under heated conditions have been changed slightly compared to unheated conditions. Ultimately, a proper placement of the flow measuring device was determined to measure the flow rate accurately.