This work aims to report the cyclopentane(CP)-carbon dioxide binary sII hydrate phase equilibrium data in the presence of aqueous sodium chloride solutions at five different mass fractions (0.00, 0.035, 0.07, 0.10, 0.15 and 0.25) in the range of temperature from (269.8 to 292.4) K and pressure from (1.18 to 3.33) MPa. An isochoric pressure-search method is applied for the experimental measurements. The obtained equilibrium data of CO 2 hydrate in pure water are compared with those from the literature. The good agreement validates that our experimental apparatus and approach are well-established and reliable. It is indicated that the inhibiting effect of NaCl yields to the promotion effect of cyclopentane except for the case of 0.25 mass fraction of aqueous NaCl solution.