Mixed matrix membranes (MMMs) consisting of multiwalled carbon nanotubes (MWCNTs) embedded within polyetherimide were prepared. Surfactants of different charges were utilized to disperse the nanotubes through a simple non-covalent approach. The characterization results suggest that proper selection of the dispersing agent contributed to better dispersion of nanotubes. The MMMs exhibited improved thermal stability and mechanical strength, which indicate the improvement of dispersion and compatibility within the polymer matrix. The resulting membrane exhibited permeance improvement of O2 and N2 as much as 87.7% and 120% respectively compared to that of neat polyetherimide. The results implied that Triton-X100 treated MWCNTs is a promising filler to enhance gas permeability.