The present invention addresses the problem of providing a pharmaceutical preparation composition which is a pharmaceutical preparation containing a polymerized camptothecin derivative produced by bonding a camptothecin derivative capable of associating in an aqueous solution thereof to form nano particle to a polymer carrier, and which has improved pharmaceutical stability. Particularly, the present invention addresses the problem of providing a pharmaceutical preparation capable of maintaining the nano particle-forming property thereof, which is an important factor, and having excellent storage stability. A pharmaceutical preparation which contains a block copolymer composed of a polyethylene glycol segment and a polyglutamic acid segment linked to each other, wherein the polyglutamic acid segment contains a glutamic acid unit having a camptothecin derivative bonded thereto. In an aqueous solution of the pharmaceutical preparation, associations can be formed. When the pharmaceutical preparation is prepared into an aqueous solution containing the camptothecin derivative at a concentration of 1 mg/mL, the aqueous solution has a pH value of 2.4 to 7Ø In the pharmaceutical preparation, the rate of change in the ability of forming the associations after the pharmaceutical preparation is stored at 40°C for 1 week under light-blocked conditions is 50% or less.
