Provided is a water-containing fluid composition comprising a processed lysozyme and/or a salt thereof, the water-containing fluid composition having a fluorescence intensity specified below of 5000 or more, wherein the processed lysozyme and/or the salt thereof is dissolved in the water-containing fluid composition while being in contact with a polar organic solvent, and a content of the polar organic solvent in the water-containing fluid composition is 55 mass% or more and 90 mass% or less. The fluorescence intensity: a fluorescence intensity measured under conditions of an excitation wavelength of 390 nm (excitation bandwidth of 10 nm) and a fluorescence wavelength of 470 nm (fluorescence bandwidth of 10 nm), for a solution obtained by adding 25 µL of an 8 mM solution of 1,8-anilinonaphthalenesulfonic acid in methanol to 5 mL of a diluted solution obtained by diluting the water-containing fluid composition with a phosphate buffer solution (pH 7.0) to a concentration in terms of solid content of the processed lysozyme and/or the salt thereof of 0.05 mass% and a concentration of phosphate of 0.2 M, and thereafter allowing the solution to react at room temperature for 30 minutes.
