Novel hybridnanocomposites were synthesized from modified cellulose acetate butyrate (MCAB)via sol-gel reaction at ambient temperature. The inorganic phase wasintroduced in situ by hydrolysis-condensation of tetraethoxysilane(TEOS) in different concentrations, using an acid catalyst, in the presence oforganic polymer dissolved in acetone. Infrared spectroscopy (IR) was used tomonitor modification of CAB and nanocomposites characterization. The silicanetwork of obtained nanocomposites was characterized by solid state 29SiNMR. Morphology of the samples and degree of dispersion of inorganic phase inthe polymer matrix were investigated using atomic force microscopy (AFM). Theorganic-inorganic nanocomposites exhibit better mechanical properties thanunmodified cellulose acetate butyrate.