The addition of magnetic nanoparticle fillers to polymers forming mixed matrix membranes can affect gas mixture separation owing to variation of magnetic susceptibility of different gas molecules and variable interaction with the dispersed magnetic fillers that can alter separation selectivity. Herein, polymeric hollow fibers were produced from a commercial co-polyimide precursor via phase inversion, whereas carbon hollow fibers were also prepared by carbonization of the polymeric ones. Gas permeation performance of the above membranes was evaluated and compared to performance after doping the membranes with Fe-based magnetic nanoparticles introduced into the membranes as fillers and acting as "internal nano-magnets". The magnetic properties of the resulting materials were evaluated by Mossbauer spectroscopy and Squid magnetization measurements. Permeation experiments, using a series of gas molecules, namely CO2, O-2, N-2 and CH4, were also conducted. The results indicated that the introduced magnetic nanoparticles modified the gas permeance/separation properties of both the polymeric and carbon composite membranes.