High-definition automated optical analysis was used to observe the morphological changes of bleached hardwood dissolving pulp during oxidation mediated by (2,2,6,6-tetramethylpiperidn-1-yl)­oxyl (TEMPO). The effects of TEMPO treatment kinetics on fiber morphology and fibrillation degree at a constant reagent loading were studied. The pulp underwent significant swelling, and carboxyl groups were introduced in which the fiber cell walls loosened, which contributed to fibrillation and subsequently nanocellulose dispersion quality in terms of both viscosity and visible light transmittance. The use of an automated optical fiber analyzer facilitates process control, as it allows controlling the fiber morphology and preventing major losses in the form of pulp fines stemming from an unnecessarily long TEMPO oxidation time.