The interaction of free convection with thermal radiation of a viscous incompressible unsteady flow past an impulsively started infinite vertical plate in the presence of chemical species concentration and a temperature boundary condition which follows a ramp function up until some specified time and then remains constant is analyzed. The fluid is assumed to be gray, emitting-absorbing but no-scattering medium and the optically thick radiation limit is considered. The Cogley-Vincenti-Gilles formulation is adopted to simulate the radiation component of heat transfer. The dimensionless governing equations are solved using Laplace transform technique. The velocity, the temperature and the concentration profiles are shown on graphs for different gasses. The variation of skin-friction is also shown in a table. The effects of different parameters like Radiation parameter ( F ), thermal Grashof number ( Gr ), Prandtl number (Pr), Schmidt number (Sc), mass to thermal buoyancy ratio parameter ( N ) for the three cases N=0 (the buoyancy force is due to thermal diffusion only), N>0 (the mass buoyancy force acts in the same direction of thermal buoyancy force) and N<0 (the mass buoyancy force acts in the opposite direction of thermal buoyancy force) and time ( t ) are discussed. The interaction of free convection with thermal radiation near a ramped temperature plate has also been compared with the flow near a plate with constant temperature. It is observed that the velocity increases with decreasing radiation parameter. © 2010 American Institute of Physics.