A chitosan coating solution which is so safe that it is capable of oral administration in the fields of foods and medicines a chitosan coating film reduced in the content of a residual organic acid and having satisfactory water resistance and a coated medical preparation having the coating film. The coating solution is characterized by being obtained by incorporating a glycerin fatty acid ester into an aqueous chitosan solution prepared through dissolution with a volatile organic acid. The chitosan coating film is one obtained by drying and solidifying the solution through film coating. The organic acid used in the dissolution remains in the coating film only in a small amount and the film has satisfactory water resistance. When the chitosan coating solution, which contains a glycerin fatty acid ester and is a highly safe solution prepared through dissolution with a volatile organic acid, is subjected to film coating, a film is formed and, simultaneously therewith, the organic acid continuously volatilizes. Consequently, a chitosan coating film having water resistance can be efficiently obtained. Furthermore, by forming a known enteric coating film in combination with the coating film on the outer side thereof, an application to large-intestine drug delivery system preparations can be expected with ease.
