PURPOSE: To enhance the safety and stability of the title agent by preparing the liposome forming agent from the 2-[(2-hydroxy-N-alkyl)acyloxypropyl amino]ethyl phosphoric ester shown by a specified formula.

CONSTITUTION: The liposome forming agent is prepared from the 2-[(2-hydroxy- N-alkyl)acyloxypropylamino]ethyl phosphoric ester expressed by formula I (R is 8W20 C straight-chain or branched-chain alkyls, and M shows a sodium ion, a potassium ion, an ammonium ion, and a triethanolamine ion). Ultrasonic treatment, an injection method, and surfactant treatment can be applied to form the liposome from the liposome forming agent. In addition, the liposome forming agent is compatible with the organisms and is the substance having high safety.