To achieve the efficient utilization of thermal energy, the development of latent heat storage materials, which have expedient equilibrium temperatures, is essential. In the present study, we revealed the effects of C=C double bonds introduced in quaternary phosphonium cations on the latent heat storage properties of semiclathrate hydrates (SCHs). The equilibrium temperatures and the dissociation enthalpies of SCH were located at 274.8—277.5 K and 175—199 J·g-1, respectively. Both of equilibrium temperature and dissociation enthalpy were lower than those of SCHs with the corresponding normal alkyl groups. One of the main reasons is the configurational fit of the guest ions to the hydrate cages. The introduction of C=C double bonds can be a method to adjust the latent heat storage properties of SCH.