The objective of our work was to characterize natural rubber (NR) samples with different macromolecular structures by measuring Mooney viscosities (V-R) at variable rotor speeds <= 2 rpm, called variable speed Mooney viscosity (M-vs). Model samples of technically specified rubbers of constant Mooney viscosity (TSR5CV) were prepared with chosen specific clones. The structures of the samples were characterized by size-exclusion chromatography coupled with an online multi-angle light-scattering detector (SEC-MALS). Rheological properties of the samples were also characterized by a dynamic moving die rheometer. Measuring monoclonal model samples by M-vs showed three types of V-R flow curves. The V-R at high rotor speed (2 rpm) was correlated with number-average molar mass M-n), whereas V-R at low rotor speed (0.05 rpm) was correlated with weight-average molar mass (M-w). Measuring M-vs revealed the rheological behaviors of samples and enabled discrimination between samples with different macromolecular structures and should thus help in predicting processability. POLYM. ENG. SCI., 50:240-248, 2010. (C) 2009 Society of Plastics Engineers