Clay minerals such as the layered silicates montmorillonite and vermiculite, as well as the fibrous clay sepiolite, and a layered double hydroxide ([Zn2Al(OH)6]Cl·nH2O) have been used to prepare gelatin-clay micro- and nano-composites. This biopolymer can be assembled to those inorganic solids through interactions at the nanometric range, but only in the case of montmorillonite intercalation of gelatin takes place. One of the most salient features of the resulting bio-nanocomposites is the possibility to be processed as homogeneous thin films provided of good mechanical properties and transparency. The Young's modulus of gelatin-sepiolite bio-nanocomposites may increase by a factor of 2.5 with respect to neat gelatin. The incorporation of pH indicator dyes to the montmorillonite bio-nanocomposite films allows their application for optical pH sensing.