Clathrate hydrates have recently received attention as novel storage and transportation materials of natural gases. For the economical storage or transportation of the produced natural gas hydrates, the effect of sintering should be considered because the hydrate particles would be stored in relatively moderate conditions. In the present study, microscopic observations were carried out on gas hydrate particles to investigate their sintering properties. The spherical gas hydrates were prepared from spherical ice particles with carbon dioxide (CO2) or ethane (C2H6) pressures higher than the dissociation ones. The initial sintering rate of CO2 hydrates at temperatures between 271.4 K and 278.2 K and pressures between 1.9 MPa and 2.9 MPa was similar to that of THF hydrate under saturated conditions reported previously. Conversely, the C2H6 hydrate particles were hard to sinter at temperatures between 273.5 K and 281.7 K and pressures between 0.5 MPa and 2.0 MPa. We discussed the sintering process of gas hydrates and their rate-determining process which depended on guest molecules under their stable conditions. The sintering of methane hydrate particles under stable and self-preservation conditions was also investigated to demonstrate the storage and transportation conditions of natural gas hydrate particles.