Great interest is devoted to electro-optic (EO) polymers since they allow the fabrication of very high performance microwave photonic components, such as optical modulators and analog-to-digital converters, due to a much better velocity matching between microwave and optical signal as well as a higher EO coefficient than the very popular inorganic LiNbO3 material. This paper studies the influence of nanoparticle loading on optical properties of EO polymers. We are interested in the host-guest system. A proof of concept is investigated by using a polymer matrix in which we add Disperse Red One (DR1) chromophores. Our first investigations are realized with TiO2 nanoparticles, which are transparent at the telecommunications wavelength of 1.55 μm. The m-lines technique allows measuring the refractive index of the films. As expected, the refractive index increases when weight-weight percentage of DR1 to PMMA increases from 3.5 wt.% to 14 wt.%. The refractive index increase tends to saturate at high DR1 percentages, which suggests that DR1 aggregation occurs. By adding TiO2 nanoparticles, a further increase is observed that we discuss by considering both the refractive index of TiO2 and the possibility to decrease the DR1 aggregation.