The dynamic structures of expanded liquid rubidium from the triple point to near the critical point are investigated by means of a molecular-dynamics simulation with the effective pair potential obtained from the experimental structure factor by the inverse method. The results are discussed in comparison with the experimental data and also with those obtained with the effective pair potential derived by means of the pseudopotential perturbation theory. It is shown that the effective pair potential obtained from the static structure factor can reproduce fairly well the dynamic structure factor for a wide range of density up to near the critical point.