To obtain, in a high yield, a heterocyclic bis(phosphonic acid) derivative useful as a bone resorption-reducing agent by the reaction of a specific carboxylic acid derivative with phosphorous acid and phosphorus oxychloride, followed by hydrolysis.

This derivative, 1-hydroxy-2-(imidazo[1,2-a]pyridin-3-yl)ethane-1,1- bis(phosphonic acid) shown by formula II or a salt thereof, is obtained by mixing a carboxylic acid derivative shown by formula I and, preferably, 2.5-5 molar equivalents of phosphorous acid in 1-20 volume(s) of a solvent (e.g. toluene, xylene, and chlorobenzene), followed by stirring, preferably, at 80-100°C for 5-30 min, adding, preferably, 2-5 molar equivalents of phosphorus oxychloride to the resultant mixture, reacting preferably, at 80-100°C for 1-4 hr, removing the solvent, hydrolyzing the obtained residue, followed by heating and refluxing the obtained matter, preferably, in an acidic aqueous solution such as 6N HCl. Isolation and purification of the derivative are carried out by extraction, recrystallization, and so on.