The significance of protein aggregation has been extensively studied in biomedical and food research. While biomaterials derived from plant proteins, such as soy protein, as green material alternatives, have gained enormous attentions in various industrial and engineering fields including food packaging and adhesives, etc., the roles of protein aggregation in material properties and functionalities are insufficiently understood, which will be the focus of this study. In this study, soy protein isolate (SPI) with different aggregated structures, is investigated as a functional modifier to tune the micro-structures and dielectric properties of two polymers: hydrophobic poly(vinylidene fluoride) (PVDF) and hydrophilic poly(ethylene oxide) (PEO). The aggregated structures of SPIs are obtained via various controlled denaturation processes, including heat treatment, high-energy sonication, pH control, and usage of denaturation agents. Denatured SPIs are then applied to polymer matrices. It is found that SPI aggregation and SPIpolymer interactions are strongly subjected to the denaturation conditions, as well as properties of polymer matrix, which lead to distinctive morphologies and structures of the resulting polymer/SPI films. This is investigated via scanning electron microscope, confocal laser scanning microscopy, X-ray diffraction spectrum, and Fourier transform infrared spectroscopy. The changes in micro-structures consequently cause the variation of ferroelectric and dielectric properties of the films, leading to different dielectric polarization and energy storage properties. Keywords: Soy Protein; Protein Aggregation; Poly(ethylene oxide); Poly(vinylidene fluoride); Dielectric Properties; Energy Storage Performances