To provide a new cholesterol derivative which is low in toxicity to living bodies, has a high inclusion rate, high solubility in supercritical carbon dioxide, is excellent in imaging of systemic blood vessels and livers, is also excellent in imaging of pancreas, and has good such safety that most of the cholesterol derivative is excreted outside bodies within 24 hours, to provide a liposome, to provide a method for forming a liposome, and to provide a contrast medium containing the liposome and used for X-rays.

This cholesterol derivative is characterized by being represented by the general formula (1) [G represents a residue obtained by reacting a sugar with hydroxyamino group; (n) is an integer of 2 to 6], the liposome, the method for forming the liposome, and the contrast medium containing the liposome and used for the X-rays.