Micellar preparation in which the solubility of a sparingly water-soluble anticancer agent has been heightened and which after intravenous administration, enables a high blood concentration to be maintained. The preparation has high medicinal activity and/or reduced side effects, and is formed from a block copolymer represented by formula (1):[wherein R1 represents hydrogen or C1-5 alkyl R2 represents C1-5 alkylene R3 represents methylene or ethylene R4 represents hydrogen or C1-4 acyl R5 represents hydroxyl, optionally substituted aryl C2-8 alkoxyl, substituted C1-4 alkylamino, or amino having a residue of either an amino acid or a peptide derivative n is an integer of 5 to 1,000 m is an integer of 2 to 300 and x is an integer of 1 to 300 provided that the proportion of hydroxy in the R5s is 0 to 99% and x is not larger than m] and a sparingly water-soluble anticancer agent.
