We model Si60 fullerene nanocages filled with methane molecules and investigate the capacity of such endohedral fullerene for energy storage. ab initio calculations at the Density Functional level of Theory (DFT) showed that up to eight CH4 molecules being incorporated inside the cage can form the stable complex with Si60 fullerene. Our calculated results revealed a significant increase in the storage capacity of methane inside Si60 fullerenes compared with C60 fullerenes. Furthermore, the penetration of methane molecules into the Si60 nanocage seems to be substantially easier than that of the C60 nanocage, with barrier energies of about 12.13 (eV) and 70.49 (eV), respectively. Therefore, these Si60 fullerene nanocages seem to be a promising material for energy storage.