A non-destructive observation and the absolute density analysis method of air clathrate hydrates in ice core were developed. Phase-contrast X-ray CT is considered to be a powerful tool for nondestructive observation due to its high density resolution. We developed a cryochamber and a liquid cell, which enabled low-temperature X-ray CT measurements from -80°C to room temperature. The technique can be applied to the imaging of temperature-induced phase or compositional change of various materials besides various gas hydrates.