A free-standing (biomacomolecule/synthetic inorganic nanotubes) hybrid film was fabricated through an alternative layer-by-layer (LBL) assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found in volcano ash. The hybrid film thickness increased linearly with the number of the bilayers, because of the interaction between the negatively charged surface of sacran and the positively charged surface of imogolite. UV-vis spectroscopy indicated that the LBL film exhibited good transparency. The surface morphology of the LBL film was smooth in the micrometer scale; many imogolite nanotubes were adsorbed onto the sacran layer, while no imogolite clusters were observed. Furthermore, the structure, stability, gas permeability, and mechanical properties of the LBL films were investigated.