An expression for the radiation pressure in high density plasma is derived on the basis of plasma waves and semiclassical theory of radiation. Comparison of our result with that of Planck, Sommerfeld and Landau and Lifshitz is briefly discussed. It is shown that the radiation pressure in a high density plasma is not just one third of the corresponding energy density because of the different dependence on the index of refraction n(omega). Possible applications to the thermal history of early universe and late stage stellar evolution are also stressed.
