Adding varieties of nanoparticles to the base fluid is a recent technique for boosting the thermal performance of mono-nanofluids and conventional fluids. The main intension of this article is to investigate the forced convection heat transfer of water-based Al2O3 nanofluid and Al2O3 + graphene hybrid nanofluid numerically. Selected volume concentrations of Al2O3/water nanofluid (0.3, 0.6, and 1.0 vol%) has been compared with Al2O3 + graphene hybrid nanofluid. The working fluids were tested in three different sizes of mini tubes, i.e., 2.1, 1.1, and 0.8 mm. The homogeneous model was breezed to simulate the hybrid nanofluids. Thermophysical and rheological properties of the nanofluids were taken from standard experimental tests which are available in the literature to validate toward computational study. The results clearly indicate usage of Al2O3/water nanofluid greatly enhances convection heat transfer performance in mini tube. A high enhancement in heat transfer coefficient by adding 0.0175 vol% graphene nanosheets was performed in simulation, which provide a range between 12.7 and 13.7% over Al2O3/water nanofluids. However, the divergence of impact for adding graphene on Al2O3 nanofluids was marginal with change in mini tube sizes. Moreover, extra penalty in pressure drop was noted. © 2019, Shiraz University.