Flow and heat transfer characteristics of Mn-Zn ferrite magnetic nanofluid are evaluated inside a circular pipe under the effect of quadrupole magnetic field. The numerical solution is performed using the Eulerian-Lagrangian method at different Reynolds numbers, particle sizes, mean concentrations and magnetic field magnitudes. Application of the quadrupole magnetic field causes the nanoparticles to move towards the wall and makes the concentration distribution more uniform at the pipe cross section. Furthermore, as the nanofluid proceeds along the pipe, the concentration distribution becomes more uniform in the section of applying magnetic field. This will in turn increase the convective heat transfer coefficient and this increment becomes more significant at greater magnetic field magnitudes. The results show that in the presence of the magnetic field, increasing the particle size raises the convective heat transfer. Furthermore, in the section of applying magnetic field, the effect of concentration increment on the convective heat transfer is greater than the sections without magnetic field. Moreover, application of the magnetic field increases the pressure drop within the pipe. (C) 2016 Elsevier B.V. All rights reserved.