PROBLEM TO BE SOLVED: To provide a production method to improve the solubility of imidazopyrroloquinoline in water and also improve the thermal stability.SOLUTION: This invention provides alkali metal salt of imidazopyrroloquinoline (IPQ), also known as 7,10-dihydro-7-oxo-imidazo [4,5,1-ij]pyrrolo [2,3-f]quinoline-1,3,9-tricarboxylic acid, and a production method thereof.