Abstract: The strength of the CO2 hydrate membrane that forms at the interface between liquid CO2 and artificial sea water at 40–45 MPa was measured with Du-Nouy type surface tension meter. At low temperatures with a subcooling greater than 5 K, the membrane strength, initially abut 0.1 N/m, decreased with increasing temperature. However, it increased sharply and reached a peak of about 0.9 N/m just below the dissociation temperature and abruptly drops to zero at the dissociation temperature. This abnormal tendency of the membrane strength was previously observed by the authors in an experiment with fresh water. The temperature of the abnormality, however, shifts to lower temperatures and the peak decreases with increasing salinity. This new phenomenon could exert major influences on the various CO2 ocean sequestration methods that have been proposed to mitigate global warming. It can be explained in terms of a model in which the dissociation process of hydrate that occurs near the dissociation temperature enhances the diffusion of water molecules in the hydrate membrane and makes the membrane thicker.