Bulk viscosity and mutual coefficients of hard sphere (HS) mixtures predicted by kinetic theory are compared with molecular dynamics (MD) results. While for the mutual diffusion only the isotopic 2-component system is considered, for the bulk viscosity, both isotopic and systems composed of differently sized HS's are investigated. The results are interesting in two respects:1.for the isotopic mixture, value and concentration dependence of the mutual diffusion coefficient given by kinetic theory agree well with the ‘exact’ MD data.for mixtures composed of differently sized particles, kinetic theory predicts slightly higher bulk viscosity compared with the MD data, but gives correct trends for the concentration dependence.