Abstract: A casein-containing water-soluble film is provided, which is useful for packaging applications and is excellent in water solubility, film strength, stretchability, formability, and sealability. A chemical agent package is also provided, which is produced by packaging a chemical agent with the water-soluble film. The water-soluble film contains casein and/or a casein salt, a polyvinyl alcohol resin (A), and a plasticizer (B), wherein the polyvinyl alcohol resin (A) includes a cationic polyvinyl alcohol resin and/or a nonionic polyvinyl alcohol resin, wherein the content ratio (mass ratio) of the casein and/or the casein salt to the polyvinyl alcohol resin (A) is 15/85 to 45/55, wherein the plasticizer (B) is present in a proportion of 15 to 60 parts by mass based on 100 parts by mass of the polyvinyl alcohol resin (A).