The stability of azithromycin sodium dihydrogen phosphate for injection was studied by TLC and bioactive test.Samples were placed under the conditions of high temperature, high humidity, or illumination for 10 d or under RH of 75% for 3 mo, or its packaged samples were placed at 40° for 3 mo, and appearance, pH, clarity and color of its solution, and content of decomposed products were observed and measured.The results showed that azithromycin sodium dihydrogen phosphate for injection was stable.