Flow of Williamson nanofluid over a stretching sheet is addressed. Entropy generation is modeled by second thermodynamics law. Present model examines the momentum, heat, mass and entropy generation. Joule heating, viscous dissipation and chemical reaction are considered in the modeling. Fluid is conducting electrically through applied magnetic field. Optimal homotopy analysis method is implemented for the solutions. Series solutions convergence by residual errors is ensured. Outcomes of magnetic parameter. Prandtl number, Brownian motion, chemical reaction parameter, thermophoresis and Brinkman number are examined. Moreover coefficient of skin friction and heat transfer rate (Nusselt number) are computed and examined. Heat transfer rate by Brownian parameter is increased. Furthermore entropy generation rate increases for higher magnetic parameter. (C) 2019 Elsevier Ltd. All rights reserved.