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Forsterite (Mg2SiO4) ceramics are excellent candidate materials for components operating with high-frequency electromagnetic waves, due to their low dielectric losses. In this paper, we discuss a novel processing approach for the production of forsterite monoliths based on the mixing of silicone resins with MgO nano-sized particles. The interaction between the nano-sized filler and the silica provided by the oxidative decomposition of silicones was so effective that forsterite formed at only 800 °C, i.e., just above the transformation temperature of the preceramic polymers. The approach based on silicones modified with oxide fillers was followed also when trying to suppress undesirable phases, such as unreacted MgO and enstatite (MgSiO3); in particular TiO2, added in form of nano- and micro-sized powders, was useful both as active filler, promoting the formation of forsterite solid solution and Mg-titanates, and as passive filler, leading to a forsterite/rutile composite. Both Ti-doped forsterite and the composite featured interesting dielectric characteristics (low dielectric constant, high quality factor), despite the presence of some residual porosity (≈15%, after firing at 1100 °C).