A mathematical model is presented to study the role of an applied magnetic field on heat transfer in a fluid flow over a stretching surface in the presence of temperature dependent viscosity. A similarity transformation is used to reduce the governing partial differential equations into ordinary ones, which are solved numerically by shooting method. Numerical results for the velocity and temperature profiles as well as for the skin friction and Nusselt number are obtained and reported graphically for various parametric conditions to show interesting aspects of the solution.