Poly(methyl methacrylate)-silica hybrid materials (PMMA-SiO2) were prepared by in situ polycondensation of alkoxysilane in the presence of trialkoxysilane-functional PMMA. Infrared, differential scanning calorimetry, Si-29 and C-13 nuclear magnetic resonance spectroscopy, and thermogravimetric analysis were used to study the PMMA-SiO2 hybrids. The effects of the content and kind of the alkoxysilane on the dynamics and stability of the PMMA-SiO2 hybrids were investigated in this study. The dynamics of SiO2 within hybrids were investigated with Si-29-H-1 cross-polarization. The spin-diffusion path length was on a nanometer scale estimated with the spin-lattice relaxation time in the rotating frame (T-1p(H)). The apparent activation energies for the degradation of the hybrids under air and nitrogen were evaluated by the van Krevelen method.