New nanosized silica with the propane lithium sulfonate was systematically synthesized as the lithium ions source of the single ion conductor. The cross-linked single ion conductor based on the PEGDMA, the modified silica, and the plasticizer (PC/DMSO, 50/50 w/w) was prepared by UV-curing. Ionic conductivity and interfacial stability toward the lithium electrode of the cross-linked nanocomposite single ion conductor were investigated by varying the modified silica content. The ionic conductivity of the cross-linked single ion conductor showed maximum trend with the modified silica content. The ionic conductivity of the cross-linked single ion conductor with 30% modified silica was 2.2×10−4 S/cm at 25 °C. Interfacial stability between the cross-linked nanocomposite single ion conductor and the lithium electrode was enhanced by introducing the modified silica.