PURPOSE: To provide a liposome preparation containing a highly pure natural phospholipid as a phospholipid and a lipo-soluble platinum complex as an active ingredient, prevented in the aging decomposition of the platinum complex and having an excellent anti-cancer activity.

CONSTITUTION: The subject liposome preparation contains a highly pure natural phospholipid having a phosphatidylcholine content of ≥90%, preferably ≥95%, as a phospholipid forming the liposome and a lipo-soluble platinum complex of the formula (R1, R2 are organic group-substituted or -nonsubstituted ammine which may be substituted through a divalent organic group; R3 is saturated or unsaturated higher fatty acid residue) as an active ingredient. The phospholipid is preferably highly pure purified soybean lecithin or highly pure purified york lecithin. In order to stably store the liposome, the liposome preparation is preferably lyophilized, or substituted with nitrogen gas when prepared, and further preferably set to an initial pH of 6-7.