This article presents numerical investigation of the heat transfer behavior of Al₂O₃/water nanofluid flow through helical tubes. Temperature-dependent thermal conductivity and the Brownian motion of nanoparticles in the nanofluid have also been taken into account. The results obtained indicate that the addition of nanoparticles into the base fluid will enhance the overall heat transfer coefficient in helical tubes. It was also concluded that the amount of increase in overall heat transfer coefficient with the addition of nanoparticles to the base fluid in a helical tube with smaller pitch circle diameter is more than a helical tube with higher pitch circle diameter.