The interest in “green” materials, or materials made with biocompatible and biodegradable components is growing, including research into natural polymers, namely proteins and polysaccharides, due to their structures and properties. Soy protein isolate (SPI) has shown promise as a modifier for polymer composites with broad applications. However, little is known about how these protein structures following the denaturation and re-aggregation processes during material processing affect their interactions with one another as well as with the polymer matrix. This study intended to achieve better understandings on this research problem by exploring relaxation behaviors of polyethylene oxide (PEO)/SPI composites via rheological and dielectric analyses. Composites of different SPI concentrations were fabricated in three ways: ball milling (BM), solution processing with deionized water (H$_2_2$0 composites achieving higher dielectric constant than PEO/SPI-DMSO composites. The α-relaxation of PEO was substantially affected by both PEO-SPI interactions and the presence of SPI networks. While the PEO-SPI interactions favored α-relaxation, the SPI network structures had the opposite effects, to different levels subjected to materials processing.