instead of aspoxicillin salt and thereby the aspoxicillin salt is formed when they are dissolved in the distilled water the aspoxicillin used in this invention may be in the form of an amorphous anhydride or a crystalline trihydrate the basic substance includes for example alkali metal hydroxides e g potassium hydroxide sodium hydroxide etc alkali metal carbonates e g potassium carbonate sodium carbonate etc alkali metal hydrogen carbonates e g potassium hydrogen carbonate sodium hydrogen carbonate etc basic amino acids e g lysine arginine ornithine etc trishydroxymethylaminomethane and the like particularly preferred basic substances are sodium hydroxide potassium hydroxide and sodium carbonate when aspoxicillin and aspoxicillin salt are used for preparing the desired preparation these are used in a ratio of about 0 7 to 7 mole of aspoxicillin to 1 mole of aspoxicillin in case of preparing the preparation by using aspoxicillin and a basic substance the basic substance is used in an amount of about 0 4 to 0 88 mole to 1 mole of aspoxicillin by which the aspoxicillin salt is formed in an amount of about 0 7 to 7 mole to 1 mole of aspoxicillin when they are dissolved in the distilled water for injection besides within the above.