One of the main drawbacks of biodegradable poly(ethylene succinate) (PES) is its slow crystallization rate. We prepared three nanocomposite samples in the present work by incorporating different small amounts of octavinyl-polyhedral oligomeric silsesquioxanes (ovi-POSS) into the PES matrix. The morphology and dispersion of ovi-POSS were first studied with a scanning electron microscope in the PES matrix. The nanofiller showed a nice dispersion throughout the polymer matrix with a regular structure, indicating the crystalline feature. The influences of different amounts of ovi-POSS on the nonisothermal and isothermal crystallization behaviors, spherulitic morphologies, and crystal structures of the nanocomposites were extensively investigated with several techniques. Ovi-POSS obviously enhanced the crystallization behaviors of PES as an efficient nucleating agent in the nanocomposites; moreover, the nanocomposites and neat PES had the same crystal structures and crystallization mechanisms.