The optical properties of the isoelectronic compounds LaCoC3 and HoCoO3 have been experimentally and theoretically investigated. We have measured the real (ε1(ω)) and imaginary (ε2(ω)) parts of the dielectric function, the reflectance R(ω) and the optical conductivity at room temperature. A shift of the most pronounced spectral features to the high energy region by 0.3 eV associated with larger distortions due to the smaller rare earth ionic radii in HoCoO 3 in comparison with LaCoO3 was observed. Also there was found an enhancement of the absorption intensity in the range 1.3-2.3 eV in all kinds of spectra of HoCoO3, which can be attributed on the basis of the results of LDA+U calculations to the different spin states of the Co 3+ ion in these compounds. The shift of the onset of the absorption from less than 0.1 eV in LaCoO3 to 0.7 eV in HoCoO3 and an absorption intensity enhancement in a narrow spectral range 1.2-2.6 eV in HoCoO3 are clearly seen from the calculated convolution of partial densities of states obtained in the LDA + U approach. Such changes are assumed to be induced by the different Co3+ spin states in these compounds at room temperature.