The controlled dispersion of Stöber silica nanoparticles (SiNPs) at the interface of a PS/PA6 (80/20 wt%) blend was achieved by means of surface modifications using 3-methacryloxypropyltrimethoxysilane (MPS). The final localization of SiNPs in the blend was predicted using wetting parameter calculation and confirmed by scanning electronic microscopy (SEM) observations. Stability of blends during annealing was evaluated qualitatively by laser diffraction particle size analyzer. Morphologies of the blends in the molten state were observed using optical microscopy. Flammability of blends was investigated using pyrolysis-combustion flow calorimeter (PCFC). Results showed that both microstructure stability during annealing and thermal degradation of the blend, were improved when MPS-modified SiNPs are located at the interface. SEM pictures revealed that the MPS-modified SiNPs form a solid barrier between PS and PA6 phases which inhibits coalescence process and modifies the thermal degradation mechanisms.