Naturally occurring polysaccharides, such as cellulose, hemicellulose, and chitin, have roles in plant skeletons and/or related properties in living organisms. Their hierarchically regulated production systems show potential for designing nanocomposite fabrication using engineered microorganisms. This study has demonstrated that genetically engineered Gluconacetobacter hansenii (G. hansenii) individual cells can fabricate naturally composited nanofibrils by simultaneous production of hyaluronan (HA) and bacterial cellulose (BC). The cells were manipulated to contain hyaluronan synthase and UDP-glucose dehydrogenase genes, which are essential for HA biosynthesis. Fluorescence microscopic observations indicated the production of composited nanofibrils and suggested that HA secretion was associated with the cellulose secretory pathway in G. hansenii. The gel-like nanocomposite materials produced by the engineered G. hansenii exhibited superior properties compared with conventional in situ nanocomposites. This genetic engineering approach facilitates the use of G. hansenii for designing integrated cellulose-based nanomaterials.