Forced convective heat transfer of an Al2O3/water nanofluid, having different shapes of nanoparticles including blade, brick, cylindrical, platelet, and spherical, flowing in a three-dimensional (3D) equilateral triangular duct has been studied numerically. The Al2O3 nanoparticle is dispersed with a ratio of 1.0%, 2.0%, and 3.0%. The Reynolds number is in the range of 100-500. A constant heat flux of 420 W/m(2) is delivered to the whole walls. The analysis is made for determining how the heat transfer and flow features are affected by different nanoparticle shapes and volume fractions. Convective heat transfer coefficient, Nusselt number, Darcy friction factor, pumping power, and performance evaluation criterion (PEC) in the duct are analyzed. The results of the study reveal that the nanoparticle shape of the platelet shows the greatest heat transfer enhancement. At the highest Reynolds number, the average Nusselt number enhances up to 25% by using platelet nanoparticle shape when compared to the pure water. Also, heat transfer in the duct increases by increasing the nanoparticle volume fraction. Also, the study is compatible with the outcomes of literature regarding heat transfer and flow features.