Numerical analysis by using Fluent® has been carried out to investigate the pressure drop of single phase flow in a 2 meter long of rifled tube and smooth tube which is placed horizontally. The rifled tube or also known as spiral internally ribbed tube that is used in this investigation has an outside diameter 45.0 mm and inside equivalent diameter1 of 33.1 mm while the smooth tube has an outside diameter 45.0 mm and inside diameter 34.1 mm. The working fluid that is used in this investigation is water. In this numerical analysis, realizable k-epsilon model has been chosen to solve the fully developed turbulence flow in both the tubes. The result of the pressure drop which is obtained from simulation shows that the pressure drop in rifled tube is about 1.69-1.77 times much higher than pressure drop in smooth tube. The high pressure drop in rifled tube comparing to smooth tube is due to the helical rib in the rifled tube which causes swirling effect near the wall. A correlation has been proposed for the single phase friction factor of the rifled tube.