Abstract: A novel spectrophotometric method for the determination of methylene diphosphonate in a stannous methylene diphosphonate kit via complex formation with iron(Ⅲ) chloride was established. The results show that the absorbance of complex obeys the Lambert-Beer law in the range of methylene diphosphonate mass concentration of 0.02-0.08 g/L, and the linear regression equation is y=14.61x+0.029 7, with the correlation coefficient of 0.999 1. The recoveries are 98.8%-102.0%, and the relative standard deviation is 0.97%(n=6). The proposed method is rapid, simple and sensitive, and therefore can be applied for routine analyses and quality control of methylene diphosphonate in its lyophilized kit.