The unique performance of natural materials stems from their hierarchical hybrid structures formed through self-assembly. The self-assembly principles of natural materials have been exploited to create artificial materials. Herein, we demonstrate a bottom-up approach that produces polymer nanocomposites as well as a self-assembled nanoenhancer for tailoring the polymer properties. The polymer is a poly(ethylene glycol) (PEG), and the nanoenhancer is aggregates formed by self-assembly of a hybrid. The hybrid is prepared through covalent bonding of a surfactant-encapsulated polyoxometalate (S-POM) complex with a PEG chain and can form aggregates composed of an S-POM complex bilayer sandwiched by two PEG layers. The lateral size of aggregates changes, depending on the conditions used in the sample preparation. Hence, we examined four nanostructures in the solid samples of nanocomposites: hybrid self-assembled nanosheets, PEG crystallized lamellae, PEG/hybrid cocrystallized lamellae, and hybrid crystallized lamellae. Because of a strong interaction among the S-POM complexes as well as good miscibility of the PEG layers with the PEG matrix, the stable aggregate homogeneously disperses in the melted PEG matrix, and hence it can enhance the performance of the melted PEG. For instance, the shear storage moduli of nanocomposites are adjustable over many orders of magnitude at temperatures above the PEG melting point. These findings provide a novel approach to generate synthetic nanocomposites with self-assembled enhancers that can tailor the polymer properties.