Normal spectral emissivity of liquid Si was determined by direct measurement of thermal radiations from a surface of the Si melt and a blackbody cavity. The spectral emissivity has little dependence on the wavelength. The emissivity is 0.27 for the wavelength from 500 to 800 nm and is about a half of that of solid silicon at the melting point. Temperature dependence of the emissivity is very small in the temperature range from the melting point to 1550 °C. Free‐electron model with a plasma frequency and relaxation time of the order of 1016Hz gives a good agreement with the experimental result. That indicates the dominant effect of the free electrons on the optical properties of the liquid Si. ©1995 American Institute of Physics.