Provided is a pharmaceutical preparation composition comprising a polymerized camptothecin derivative which is obtained by bonding a camptothecin derivative to a polymer carrier, and has nanoparticle-forming properties of associating in an aqueous solution, the pharmaceutical preparation composition having enhanced preparation stability. Particularly, a pharmaceutical preparation maintaining nanoparticle-forming properties, which are an important factor, and having an excellent storage stability is provided. Disclosed is a pharmaceutical preparation comprising a block copolymer in which a polyethylene glycol segment is linked to a polyglutamic acid segment containing a glutamic acid unit having a camptothecin derivative bonded thereto, the pharmaceutical preparation capable of forming associates in an aqueous solution. When the pharmaceutical preparation is made into an aqueous solution containing the camptothecin derivative at a concentration of 1 mg/mL, the pH of the aqueous solution is 2.4 to 7.0, and the change ratio of the associate-forming ability of the pharmaceutical preparation after storage at 40°C for one week under light-blocked conditions is 50% or less.
