Cellulose nanowhiskers with the high mechanical strength and aspect ratio have attracted considerable attention as reinforcements in composite materials with nanometric fillers. In this study, aspect ratio-controlled bacterial cellulose nanowhiskers (BCNWs) were prepared simply by varying the hydrolysis time. The nanowhiskers prepared from bacterial cellulose at different hydrolysis times were relatively longer than those produced from cotton and wood cellulose, even after hydrolysis for a long time in a strong acid solution. The bacterial cellulose nanowhiskers did not sediment or flocculate due to the surface acid groups that formed during hydrolysis. This was demonstrated by the phenomenon of flow birefringence. All the samples prepared by hydrolysis for 1-3 hours showed flow birefringence. Lyophilized BCNWs could also be re-dispersed in aqueous solutions, even in polar organic solvents.