The present invention aims at providing a slightly water-soluble camptothecin liposome preparation with an excellent retention in blood for a drug, which can stably hold a slightly water-soluble camptothecin compound for a long period of time, whereby hydrolysis of an α-hydroxylactone ring in blood is suppressed and the slightly water-soluble camptothecin compound is kept in a structure in which the ring is not opened and which makes the compound effective as an antitumor-active drug, and, moreover, the liability of the drug to leave a liposome is advantageously reduced, so that it is possible to maintain the drug concentration in plasma for a long period of time after administration. This object is achieved by the liposome preparation as described in the specification. The liposome preparation according to the present invention includes a liposome preparation including as lipid components for forming a membrane a phospholipid and a fatty acid, and containing as a drug a lightly water-soluble camptothecin compound.
