In designing mixed matrix membranes (MMMs) to improve gas separation performance, inorganic fillers such as titanium (IV) oxide (TiO2) nanoparticles are commonly added due to their excellent intrinsic properties and high affinity towards CO2. However, the addition of TiO2 nanoparticles causes the formation of agglomerates which deteriorate the gas separation properties of the membrane due to their high surface energy and Van der Waals forces. In this study, MMMs comprising octaisobutyl polyhedral oligomeric silsesquioxane (OPOSS) incorporated with TiO2 nanoparticles were successfully developed using phase inversion technique. MMMs were synthesized at different loadings of TiO2 and OPOSS. The effectiveness of OPOSS as a dispersant was determined by using SEM, EDS and single gas permeation analysis. The optimum amount of TiO2-OPOSS in the THF/DMAc casting solution was at 4wt TiO2 and 2wt of OPOSS, as the agglomeration of nanoparticles did not occur based on the morphology and gas separation performance. The membrane with the highest performance was achieved by 4/2-T/OPOSS, which is at 1.8 of CO2/CH4 gas selectivity. Based on the findings, it can be concluded that the OPOSS did play an important role in enhancing the dispersion of TiO2 nanoparticles in the polymer matrix as the TiO2 agglomerates were not seen upon addition of OPOSS. © Published under licence by IOP Publishing Ltd.