The aim of this paper is to study experimentally the forced convective heat transfer behaviour of Graphene oxide nanofluids inside a horizontal circular tube subject to a constant and uniform heat flux at the pipe wall. Graphene oxide (GO) nanoparticles were synthesized by the modified Hummers method. GO particles dispersed in pure water are used as the working fluid. Consideration is given to the effect of the inclusion of nanoparticles on heat transfer enhancement, thermal conductivity and viscosity in the turbulent flow. Four volume fractions of 0.05%, 0.10%, 0.15% and 0.20% are tested for GO/water nanofluids. The heat transfer within the flowing nanofluids were measured and compared with the corresponding data for base fluid (pure water). The Reynolds number is ranged from 3000 to 10000. It is found from the study that (i) heat transfer enhancement is caused by suspending nanoparticles and becomes more pronounced with an increase in the particle volume fraction, (ii) the nanofluids have substantially higher value of Nusselt number than the same liquids without nanoparticles and the Nusselt number of nanofluids increase in accordance with an increase of the Reynolds number, (iii) heat transfer coefficient of nanofluid increase with Reynolds number, (iv) the viscosity, thermal conductivity, and electrical conductivity of Graphene oxide (GO) nanofluid increase in accordance with an increase of the volume fraction.