The present study investigates the hydromagnetic flow of a nanofluid in a two-dimensional porous channels between slowly expanding or contracting walls. Assuming symmetric injection (or suction) along the uniformly expanding porous walls and using a similarity transformation, the governing flow equations are reduced to nonlinear ordinary differential equations. The resulting equations are then solved analytically by using the homotopy analysis method (HAM). The convergence of the obtained series solutions is analyzed through the minimization of the averaged square residual error. A comparison between analytical and numerical solutions is presented for the validation in both graphical and tabular forms. The results obtained by HAM are in very good agreement with numerical solutions obtained by the shooting method coupled with a Runge-Kutta scheme. The effects of various physical parameters such as wall expansion ratio, Brownian motion parameter, thermophoresis parameter, and Lewis number on flow variables are discussed. Analysis shows that for the case of contracting walls, the temperature increases for a given increase in Brownian motion parameter, and the thermophoresis parameter. In addition, the nanoparticle concentration increases with an increase in Brownian motion parameter and Lewis number. © 2014 by Begell House, Inc.