Neat polyurethane (PU) foams and polyurethane/nano tin oxide composites were prepared using in situ polymerization, blending methods. The produced nanocomposites were investigated by scanning electron microscopy, Fourier transform infrared spectra, thermal gravimetric analysis (TGA), and compression test. It was found that modification of tin oxide particles caused to make better distribution in PU foam nanocomposites. The results showed that increasing isocyanate content leading to enhance cross-link, density and compression strength of neat PU foams. Addition of SnO₂ nanoparticles in different density of PU foam showed variety effects. In low density foam increasing amount of SnO₂ nanoparticles from 0.5 to 1 wt% leaded PU foam to become soft with low strength. Moreover, TGA results of all PU foams exhibited one thermal decomposition step. Also, increasing isocyanate ratio and SnO₂ nanoparticles improved thermal stability of PU foams.