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• We report the structural, chemical, and mechanical properties of hybrid films. • Synchrotron-based microscopy verified the composition and structure of the film. • Films show high mechanical properties, thermal stability and UV-absorption ability. Organic-inorganic hybrid films were fabricated from cellulose nanofibrils (CNF) and nanosilica (5–30% wt) embedded in a chitosan (Chi) biopolymer matrix using a slow evaporation method. The self-standing films exhibited high strength and modulus up to 120 ± 5 MPa and 7.5 ± 0.4 GPa, respectively, which are remarkably high values for biopolymer/chitosan hybrids. Scanning electron microscopy showed that the nanosilica is formed of larger aggregates within the lamellar CNF network structure. This observation was further confirmed using synchrotron-based scanning transmission x-ray microscopy (STXM) with the capability to determine the spatial and chemical distribution analysis of the constituents of films. It is interesting that the thermal stability of the hybrid films improved as the nanosilica content increased. Furthermore, the nanosilica effectively filled the pores in the CNF network, thus decreasing the UV transmission and the visible light transmittance of the films. [ABSTRACT FROM AUTHOR]