Silicon powder was encased within carbon gel microspheres with different porosities by simply adding silicon powder to the water phase during the inverse emulsion polymerization of resorcinol with formaldehyde, followed by drying and carbonization. From the results of charge-discharge experiments, it was confirmed that the reversible capacity of silicon and its cycle ability could be improved through such encasement and that the degree of improvement depended on the porosity of the carbon gel matrix.