The authors studied acetylation of bacterial cellulose (BC) nanofibers to widen the applications of BC nanocomposites in optoelectronic devices. The slight acetylation of BC nanofibers significantly reduces the hygroscopicity of BC nanocomposites, while maintaining their high optical transparency and thermal stability. Furthermore, the degradation in optical transparency at elevated temperature (200 degrees C) was significantly reduced by acetylation treatment. Therefore, the acetylation of bionanofibers has an extraordinary potential as treatment for property enhancement of bionanofiber composites. (c) 2006 American Institute of Physics.