An effective liquid preparation achieves high bioavailability(BA) of physiologically active peptides or proteins, includingghrelins, that are administered as drugs. Also provided is a methodfor improving the BA of physiologically active peptides or proteins,including ghrelins, that are subcutaneously injected in aqueoussolutions. The liquid preparation contains: a physiologically activepeptide or protein, such as ghrelins, as an active ingredient； anacid solution including one or a combination of two or more selectedform the group consisting of acetic acid, lactic acid, phosphoricacid, glycine, citric acid, hydrochloric acid, propionic acid,butyric acid, benzoic acid and salts thereof； an alcohol； and apolar organic liquid including one or a combination of two or moreselected from the group consisting of N-methyl-2-pyrrolidone,dimethylformamide, dimethylsulfoxide and methylparaben.
