This paper evaluates the potential of using 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanoparticles (T-CNPs) as additives to tune the rheology of water-based acrylic resin (AR) coatings for flexible packaging applications. Three T-CNPs of T-CNF, T-MCC, and T-CNC were prepared from three starting cellulosic materials: cellulose nanofibers (CNF), microcrystalline cellulose (MCC), and cellulose nanocrystals (CNC), respectively. Their sizes ranged from 20 nm to 20 lmin diameter, and 234 nm to over 500 nm in length. The oxidation imparted carboxyl groups on the surfaces of nanoparticles ranging from 1.99 to 2.79 mmol/g and increased the zeta-potentials of the nanoparticles, clearly improving the dispersibility and stability of the CNPs in AR. The AR/T-CNP dispersion showed unreduced transparency. The morphologies of the T-CNPs affected the rheological properties of the AR/ T-CNP dispersions. The larger aspect ratio of T-CNF and T-MCC resulted in the high viscosity and solid-like viscoelastic behavior of the AR/nanoparticle dispersions at a concentration of 0.78 wt%. The CNC and T-CNC with a smaller particle size and aspect ratio had less effect on the viscosity and rheological behavior of the resulting dispersions compared with the others—even at a high content of 1.30 wt%. Due to a lower aspect ratio but a relatively large particle size, the AR/T-MCC dispersions exhibited elastic gel-like rheological properties at a low content.