We investigated the electronic structure of multiferroic hexagonal RMnO 3 (R = Gd, Tb, Dy, and Ho) thin films using both optical spectroscopy and first-principles calculations. One of the difficulties in explaining the electronic structures of hexagonal RMnO 3 is that they exist in nature with limited rare earth ions (i.e., R = Sc, Y, Ho -Lu), so a systematic study in terms of the different R ions has been lacking. Recently, our group succeeded in fabricating hexagonal RMnO 3 (R = Gd, Tb, and Dy) using the epitaxial stabilization technique [Adv. Mater. 18, 3125 (2006)]. Using artificially stabilized hexagonal RMnO 3 , we extended the optical spectroscopic studies on the hexagonal multiferroic manganite system. We observed two optical transitions located near 1.7 eV and 2.3 eV, in addition to the predominant absorption above 5 eV. With the help of first-principles calculations, we attribute the low-lying optical absorption peaks to inter-site transitions from the oxygen states hybridized strongly with different Mn orbital symmetries to the Mn 3d 3z 2 -r 2 state. As the ionic radius of the rare earth ion increased, the lowest peak showed a systematic increase in its peak position. We explained this systematic change in terms of a flattening of the MnO 5 triangular bipyramid.