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.