Cellulose nanocrystals (CNC) have recently received much attention in the global scientific community for their unique mechanical and optical properties. Here, we conducted the first detailed exploration of the basic properties of CNC, such as morphology, crystallinity, degree of sulfation and yield, as a function of production condition variables. The rapid cellulose depolymerization and sulfation reactions under concentrated acid concentrations of around 60 wt% resulted in a very narrow operating window for CNC production. We found that CNC yields as high as 70 wt% from a bleached eucalyptus kraft pulp with glucan content of 78 wt% can be achieved under a tight range of reaction conditions and that a weighted average length of over 200 nm and sulfur content (a measure of CNC surface charge) between 3 and 10 mg/g can be produced. This study provided critical knowledge for the production of CNC with characteristics tailored for different specific applications, significant to commercialization.