Observations of large property changes in the presence of nanoparticles have motivated an increasing interest towards the interfacial effect in polymer nanocomposites. In this work, the interface between poly(ethylene oxide) (PEO) and silica (SiO2) was modulated by the inclusion of SiO2 with three different surface functionalities, namely unfunctionalized SiO2 (SiO2-OH, grafting density = 0 chains/nm(2)), PEO-grafted SiO2, SiO2-g-PEO-1.1 (grafting density = 1.1 chains/nm(2)) and SiO2-g-PEO-2.2 (grafting density = 2.2 chains/nm(2)), and the interfacial effect on crystallization behavior of PEO/SiO2 nanocomposites was studied by the combination of differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) analysis. In contrast to the unfunctionalized SiO2, PEO grafting imparts SiO2 with a high nucleation ability, even though SiO2-OH demonstrates more homogenous dispersion in PEO matrix than PEO-grafted SiO2. The overall crystallization rate of PEO/SiO2 nanocomposites follows the order PEO/SiO2-g-PEO-2.2 > PEO/SiO2-g-PEO-1.1 > PEO/SiO2-OH. These results highlight the role of grafted chains on crystallization. It is speculated that the interfacial structure, as a function of grafting density, plays a critical role in the formation of nuclei, which ultimately determines the crystallization behavior. This work can contribute to understanding the interfacial effect in polymer nanocomposites and is believed to provide theoretical guidance for manipulating the properties of materials.