Densities and refractive indices of molten alkali iodides, MI (M = Li, Na, K, Rb, and Cs), were measured precisely by dilatometry and goniometry with visible lights, respectively. The densities of the molten iodides varied with the rise of temperature, from which the molar volumes were approximated into linear functions of temperature. The refractive indices were expressed as functions of both temperature and wavelength of the lights used, often called dispersion formulae, according to nonlinear least-squares regression. The electronic polarizabilities of discrete ions in the melts were estimated from the densities and the refractive indices extrapolated to infinite wavelength using the Lorentz-Lorenz equation.