Mixed-matrix membranes containing both two-dimensional (ns-CuBDC) and three-dimensional (ZIF-8) metal-organic frameworks were fabricated to investigate their potential capabilities in CO2/CH4 separation. The mixed-matrix membrane containing ns-CuBDC alone was capable of improving CO2/CH4 selectivity whereas the mixed-matrix membrane containing ZIF-8 alone ensured improved CO2 permeability. However, by combining both fillers in a mixed-matrix membrane aimed at tailoring the CO2/CH4 separation properties, both CO2 permeability and CO2/CH(4)selectivity were successfully improved by 16.6% and 30.5%, respectively, which indicates a highly desirable method of performance enhancement. Analysis of solubility-diffusivity in the mixed-matrix membranes revealed that the use of both fillers could improve both solubility selectivity and diffusivity selectivity. Our overall results imply that the separation properties of gas separation membranes can be readily adjusted to meet the requirements of real-world applications by the combined use of two fillers with different geometries.