Physical and structural properties of the raw polymer lots used for rubber compounds dictate bulk compound behavior. The most influential factors include molecular weight, molecular weight distribution, and the degree of long-chain branching. Rheological characterization utilizing the Rubber Process Analyzer (RPA) provides a quick and easy method to obtain these properties, delivering a means to understand and develop polymer structure and bulk property relationships. The manufacturing process and mixing history have also been shown to affect rubber compound behaviors, such as processability, viscoelastic characteristics, curing properties, and physical properties of the fully cured product. Many of these differences are likely due to changes in the polymer microstructure brought about by processing operations. In this talk we will demonstrate the capabilities of the RPA for characterizing the viscoelastic properties of natural rubber compounds and will correlate them to changes in the polymer microstructure brought about by mixing protocols. In particular, previously-established methods will be used to evaluate three different classes of peptizers. The influence of peptizers on polymer microstructure will be evaluated and correlated to subsequent compound processing characteristics. This valuable information can further be used to predict processing behavior, allowing operators to make adjustments in advance, thereby increasing productivity and reducing scrap.