The optical properties of single crystals of RNi2B2C (R=Y,Tb,Er, and Dy) were measured between 1.7 and 5.2 eV at room temperature using a spectroscopic ellipsometer. The spectra for all compounds are similar and the peak positions appear in a similar energy region. The similarity of the spectra of RNi2B2C (R=Tb,Er,Dy) to that of YNi2B2C indicates that the rare-earth 4f states are not actively involved in the optical transitions.