<p>This paper determined experimentally the crystal structures of (epoxycyclopentane + methane) and (epoxycyclopentane + hydrogen) clathrate hydrates. Using Rietveld analysis with direct space method, the crystal structure of these clathrate hydrate systems was identified as the cubic structure II (sII) clathrate hydrate, meaning the <i>Fd-3m</i> space group. With the inclusion of methane or hydrogen in the small cage of sII hydrate, there was no significant change in the lattice parameters. The microstructural analysis showed that all guest molecules were located at the center of sII hydrate cages. The structural characterization of (epoxycyclopentane + methane) and (epoxycyclopentane + hydrogen) clathrate hydrates contributed the understanding of unique nature of host–guest inclusion compounds and gave useful insights to develop the efficient CH₄ or H₂ gas storage technologies using clathrate hydrates.</p>