Organic–inorganic composite membranes were prepared from membranes of the bio-polymer bacterial cellulose (BC) and organic–inorganic sol composed of nanoparticulate boehmite and epoxi modified siloxane. Bacterial cellulose membranes are obtained in a highly hydrated state (1% cellulose and 99% cellulose) from cultures of Gluconacetobacter xylinus and could be used in the never-dried or in the dried state. Depending on the use of dried or never-dried BC membranes two main kinds of composites were obtained. In the first one dried BC membranes coated with the hybrid sol have lead to transparent membranes displaying a bi-phase structure where the two components could be easily distinguished, with individual structures preserved. A decrease was observed for tensile strength (50.5MPa) and Young’s Modulus (2.8GPa) when compared to pure BC membrane (112.5MPa and 12.7GPa). Elongation at break was observed to increase (2.5% against 1.5% observed for BC). When never-dried BC membranes were used transparent membranes were also obtained, however an improvement was observed for mechanical properties (tensile strength – 116MPa and Young’s Modulus – 13.7GPa). A lower value was obtained for the elongation at break (1.3%). In the last case the interaction between the two-phases lead to changes in the cellulose crystallinity as shown by X rays diffraction results. Multifunctional transparent membranes displaying the cellulose structure in one side and the boehmite–siloxane structure at the opposite face could find special applications in opto-electronics or biomedical areas taking advantage of the different chemical nature of the two components.