OBJECTIVE： To study the stability of baicalin magnesium salt. METHODS： The stability of baicalin magnesium salt at high temperature（60 ℃）， high humidity （90％）， strong illumination （4 000 lx）， different temperatures（20，37，50，60 ℃） and pHs（6.80，5.70，4.60，4.30，3.90，3.60，3.20） was investigated， and HPLC was used to detect the drug contents. RESULTS： High humidity test indicated that the quality of baicalin magnesium salt was increased by （6.17±0.12）％ in the 5th day and increased by （6.92±0.05）％ in the 10th day. Drug contents in the 10th day were respectively （94.78±0.12）％， （94.79±0.20）％， （94.66±0.15）％ in the high temperature， high humidity， strong illumination tests （n＝3）. In phosphate buffer solution （pH 6.80）， baicalin magnesium salt was stable only when the temperature was below 20 ℃； and it was yet stable in pure water （pH 6.76） at 37 ℃. pH stability test showed that the most stable pH was 4.30. CONCLUSIONS： Baicalin magnesium salt has hygroscopicity to some extent. Strong illumination affects the stability more seriously than high temperature and high humidity. The stability of baicalin magnesium salt in pure water is superior to in phosphate buffer solution， and the salt is stable in weak acid solution.