This work presents the kinetic promotion effect of sII cyclopentane (CP) hydrate seeds on sI CH4 hydrate formation in sodium dodecyl sulfate (SDS) solutions. Gas hydrates are one of the promising materials for natural gas storage due to their high volumetric capacity and safety aspect. Generally, a crystal layer of gas hydrate is preferentially created on the surface of an aqueous phase which results in both low hydrate conversion and slow reaction without mechanical agitations. This study introduces CP hydrate seeds at very small quantities to accelerate the nucleation and growth of the CH4 hydrate with SDS. To choose the appropriate amount of CP in the system for massive sI CH4 hydrate formation, several hydrate slurries with various amounts of CP were characterized by powder X-ray diffraction and Raman spectroscopy. Additionally, from the visual observations of the hydrate growth behavior, the direction of hydrate crystallization significantly affected the hydrate growth and conversion rate. With the highest degree of subcooling, the volumetric storage efficiency reached 90% of the theoretical values in 50 min with no induction period, and this promotion effect was also confirmed in an expanded reactor system. Thus, sII CP hydrate seeds result in a dramatic improvement in the sI CH4 hydrate formation rate and high volumetric storage capacity.