Hydrophilic silica nanoparticles (SNPs) were treated by using 3-glycidoxypropyltrimethoxy silane (GPTMS) and then they were blended with polyurethane-urea (PUU) emulsions to obtain SNPs/PUU nanocomposite films. Thermo-mechanical properties of the nanocomposite films were investigated by varying the grafted amount of GPTMS onto SNPs and the contents of SNPs in the PUU matrix. The thermo-mechanical properties of the nanocomposite films were also compared in terms of the dispersibility of SNPs in the PUU matrix and thermal curing of the GPTMS-grafted SNPs. The maximum amount of grafted GPTMS was 1.99×10^(-6) mol/m2, and which covered ca. 53% of the total SNP surface area. 29Si CP/MAS NMR analyses with the deconvolution of peaks revealed the details of polycondensation degree and patterns of GPTMS in the surface modification of SNPs. The surface modification did not significantly affect colloidal stability of the SNPs in aqueous medium; however, the hydrophobic modification of SNPs offered a favorable effect on the dispersibility of SNPs in the PUU matrix as well as better thermal stability. XRD patterns revealed that GPTMS-grafted SNPs broadened the reduced the characteristic peak of polyol in PUU matrix. The composite films became rigid and less flexible as the SNP content increased from 5 wt.% to 20 wt.%. Particularly, Young’s modulus and tensile modulus significantly increased after the thermal curing reaction of the epoxy groups in the SNPs.