The numerical solution of transient natural convection flow over a vertical cylinder under the combined buoyancy effects of heat and mass transfer along with chemical reaction is presented. The governing boundary layer equations for the above flow problem of first order homogeneous chemical reaction are set up and non-dimensionalised. An implicit finite difference method is used to solve the unsteady, non-linear, and coupled governing equations. Numerical results are presented for various parameters. The unsteady velocity, temperature, concentration profiles, local and average skin-friction, Nusselt number and Sherwood number are shown graphically and are discussed for both generative and destructive reaction.