A method for producing a drug-block copolymer composite, the method comprising: mixing a poorly water-soluble drug and a block copolymer including a hydrophilic segment and a hydrophobic segment bonded together of the following formula wherein R1 is methyl or ethyl group; R2 is ethylene or trimethylene group; R3 is methylene group; R4 is formyl, acetyl, or propionyl group; R5 is one or two substituents selected from the group consisting of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, phenylpentyloxy, and -N -CO-NHR7 group, wherein R6 and R7, which may be identical with or different from each other, each represent ethyl, isopropyl, cyclohexyl, or dimethylaminopropyl group; n represents 20 to 500; m represents 10 to 100; x represents 0 to 100; y represents 0 to 100, provided that the sum of x and y is 1 or more but is not greater than m; and the number of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, or phenylpentyloxy group among the substituents for R5 is from (0.15m) to (0.70m) on the average, in one or more non-aqueous solvents; heating the mixture to a temperature of 25°C or higher; and spray-drying the resulting mixture liquid dried in a gas flow environment maintained at a temperature lower than or equal to the melting point of the block copolymer. mixing a poorly water-soluble drug and a block copolymer including a hydrophilic segment and a hydrophobic segment bonded together of the following formula wherein R1 is methyl or ethyl group; R2 is ethylene or trimethylene group; R3 is methylene group; R4 is formyl, acetyl, or propionyl group; R5 is one or two substituents selected from the group consisting of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, phenylpentyloxy, and -N -CO-NHR7 group, wherein R6 and R7, which may be identical with or different from each other, each represent ethyl, isopropyl, cyclohexyl, or dimethylaminopropyl group; n represents 20 to 500; m represents 10 to 100; x represents 0 to 100; y represents 0 to 100, provided that the sum of x and y is 1 or more but is not greater than m; and the number of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, or phenylpentyloxy group among the substituents for R5 is from (0.15m) to (0.70m) on the average, in one or more non-aqueous solvents; wherein R1 is methyl or ethyl group; R2 is ethylene or trimethylene group; R3 is methylene group; R4 is formyl, acetyl, or propionyl group; R5 is one or two substituents selected from the group consisting of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, phenylpentyloxy, and -N -CO-NHR7 group, wherein R6 and R7, which may be identical with or different from each other, each represent ethyl, isopropyl, cyclohexyl, or dimethylaminopropyl group; n represents 20 to 500; m represents 10 to 100; x represents 0 to 100; y represents 0 to 100, provided that the sum of x and y is 1 or more but is not greater than m; and the number of benzyloxy, phenylethoxy, phenylpropoxy, phenylbutoxy, or phenylpentyloxy group among the substituents for R5 is from (0.15m) to (0.70m) on the average, in one or more non-aqueous solvents; heating the mixture to a temperature of 25°C or higher; and spray-drying the resulting mixture liquid dried in a gas flow environment maintained at a temperature lower than or equal to the melting point of the block copolymer.