A film comprising as a film-forming agent an alginate salt of monovalent cation or a mixture of alginate salts containing at least one alginate salt of monovalent cation, the film-forming agent being such that a 10% aqueous solution thereof at a temperature of 20.degree. C. has a viscosity of 100-1000 mPas, as measured at a shear rate of 20 rpm by use of a Brookfield viscometer with a spindle No. 2. A method of preparing the film. The film is useful for delivery of active ingredients to a mammal.