The growing interest in polymer-based mixed matrix membranes (MMMs) in the field of gas separation encouraged the authors to fabricate MgO nanorods and cellulose acetate (MgO-X/CA) MMMs for the separation of H2/CH4, CO2/CH4, and H2/CO2 gases. The facile solution-casting, followed by solvent evaporation technique, was applied to fabricate MMMs. FE-SEM, EDS, FT-IR, XRD, DSC, and TGA characterization techniques were used to investigate the physico-chemical properties of fabricated MMMs, whereas the gas transport properties of MMMs were investigated using a gas permeation setup. Upon uniform MgO nanorods incorporation in CA polymer, the gas permeation through MMMs is improved due to disruption of the polymer chain. The influence of feed pressure and various loadings of nanorods (5, 10, and 15 wt%) on gas permeability and selectivity of CA based MMMs were investigated at 25 °C and 1–4 bar gas pressure. Based on the results, the MgO-15/CA MMMs achieved the highest H2 permeability of 77.80 Barrer which is higher than pure CA by 45%, with a two-fold increase in H2/CO2 selectivity and unchanged H2/CH4 selectivity. Meanwhile, MgO-5/CA MMMs revealed the highest CO2 permeability of 62.90 Barrer with an increased in CO2/CH4 selectivity from 22.30 to 24.30.