The aim of this work is to study Soret and chemical reaction effects on laminar mixed convection boundary layer flow, heat and mass transfer past a semi-infinite horizontal flat plate in the presence of heat generation. A transformation is introduced, which reduces the equations governing the flow to a system of non-linear coupled ordinary differential equations. The transformed equations are solved numerically using the fourth order Runge-Kutta integration scheme coupled with the shooting method. Graphical results for the velocity, temperature and concentration profiles for various parametric conditions are presented and studied. The effect of the chemical reaction parameter, Soret parameter and the heat generation parameter on the local skin-friction coefficient, the local Nusselt number and the local Sherwood number are presented in tabular form and discussed. Keywords: Soret effect; Mixed convection; Heat generation; Chemical reaction.