This paper investigates heat and mass transfer of a MHD Casson fluid over a permeable stretching surface in the presence of a temperature gradient heat sink. The effects of viscous dissipation, thermal radiation and chemical reaction are also taken into the consideration. The relevant similarity transformations are used to reduce the governing equations into a system of nonlinear ordinary differential equations and then solved analytically. The influence of various physical parameters on the  velocity, temperature, concentration, skin friction coefficient, Nusselt and Sherwood numbers are investigated. The numerical results of skin friction factor, Nusselt and Sherwood number are compared with the previously published data for special cases and are found to be in good agreement.