The viscosities of cottonseed oil (CSO) and cottonseed biodiesel (CSB) were measured at atmospheric pressure and temperatures from (293 to 373) K and (303 to 348) K, respectively. The Vogel-Fulcher-Tammann (VFT) and Mauro (MYEGA) equations were selected to represent the temperature dependence of the experimental data, giving deviations within the experimental uncertainties. These equations allowed estimating the glass transition temperatures, which were compared with available values from literature. For viscosity prediction, the group contribution method proposed by Ceriani was compared with the fragment approach given by Zong for CSO. For CSB the Grunberg-Nissan equation coupled with Ceriani and Yuan models was applied, and the influence of the interaction parameter (G(ij)) is highlighted.