This work reports numerical simulation for three dimensional laminar mixed convective heat transfers at different nanofluids flow in an elliptic annulus with constant heat flux. A numerical model is carried out by solving the governing equations of continuity, momentum and energy using the finite volume method (FVM) with the assistance of SIMPLE algorithm. Four different types of nanofluids Al2O3, CuO, SiO2 and ZnO, with different nanoparticles size 20, 40, 60 and 80 nm, and different volume fractions ranged from 0% to 4% using water as a base fluid were used. This investigation covers a Reynolds number in the range of 200 to 1000. The results revealed that SiO2–Water nanofluid has the highest Nusselt number, followed by Al2O3–Water, ZnO–Water, CuO–Water, and lastly pure water. The Nusselt number increased as the nanoparticle volume fraction and Reynolds number increased; however, it decreased as the nanoparticle diameter increased. It is found that the glycerine–SiO2 shows the best heat transfer enhancement compared with other tested base fluids.