To provide an industrially advantageous method for inactivating endotoxin activity in a fat emulsion for the purpose of supplying nutrition to be administered to a human or in a liposome preparation used for a drug delivery system.

This method for inactivating the endotoxin in the fat emulsion or liposome preparation is characterized by heat-treating the fat emulsion or liposome preparation at 100-125°C. The heating time in this case is 5-60 min to complete the purpose, and a generally used heating device such as an autoclave can be adopted. In the fat emulsion or liposome preparation, other components such as glucose can be co-present as far as not causing coagulation by mixing them.