The morphology of cellulose nanofibrils (CNFs), the rheological characteristics of their dispersions, and the corresponding relationships, are fundamental for understanding the properties of the material. This work aims at understanding how the morphological characteristics of the CNFs affect the rheology of the dispersions in the dilute region and to establish a relationship between both properties. A strong relationship was observed between the intrinsic viscosity of the CNF dispersions and their aspect ratio, which can be correlated through the expression ρ[η]=0.051p1.85. When comparing the model obtained in this work to the wormlike chain model, it was possible to verify that these models are independent of the flexibility of the CNFs. Regarding the fibrillation process, the dynamic viscosity only reflects part of the behavior of the morphological properties of the CNFs and does not provide reliable data that would allow these characteristics to be inferred, while the intrinsic viscosity does allow this relationship.