The effect of TiO2 nanoparticles on the gas separation properties of polyurethane has been investigated. Polyurethane was synthesized using hexamethylene diisocyanate (HDI) and 1,4-butanediol (BDO) as hard segment and poly(tetramethylene glycol) (PTMG, 2,000 g/mol) as soft segment. The synthesized polymer was in a 1 : 2 : 1 molar ratio of polyol:diisocyanate:chain extender through bulk two-step polymerization. PU membranes were prepared by thermal phase inversion method. Scanning electron microscopy (SEM), X-ray diffraction and Fourier Transform Infrared (FTIR) analyses characterized the prepared membranes. FTIR and SEM results indicate the good interaction between particles and polymer matrix and also the nanoscale dispersion of TiO2 particles in polymer matrix. Gas permeation properties of PU-TiO2 nanocomposite membranes with TiO2 contents up to 30 wt% were studied for N2, O2, CH4 and CO2 gases at 10 bar and 25 ℃. Results suggest a decrease in permeability of studied gases and increase in gas selectivities as TiO2 content increases.