A CO2 hydrate power generation system for cold regions has been proposed, in which carbon dioxide hydrate is formed by cold heat from the outside air, and a generator is driven by high pressure gas obtained by dissociating the hydrate by supply of low temperature waste heat. The purpose of this study is to clarify the effect of formation reaction promoters on the improvement of carbon dioxide hydrate formation rate and increase of formation temperature upper limit. Cyclopentane, which shifts the phase equilibrium pressure curve to higher temperatures and lower pressures, was used as a formation reaction promoter in this study. This shift is expected to have the desirable effect of improving the formation rate, but adding the formation reaction promoter has the negative effect of reducing the amount of formation by reducing the amount of net water. In the experiment, a 100 ml stainless steel reaction vessel was filled with 78 ml of a two-phase solution of pure water and cyclopentane at several different volume ratios. After enough initial dissolution was performed at a desired pressure, thermal cycles of formation and dissociation were repeated by alternately flowing 273 K and 303 K heat media around the periphery of the reaction vessel. To calculate the formation rate, the measured values of pressure and temperature in the sealed reaction vessel were used, and the compression coefficient of CO2 was considered using the physical property database REFPROP. As a result, we were able to confirm that cyclopentane increased the formation rate and amount under the conditions without power stirring. This result suggests the possibility of improving the energy storage rate and the energy storage capacity per unit water volume of the proposed power generation system using cyclopentane.