A simple procedure is developed to separate Sr from a large amount of Ca, which relies on the insolubility of Ca(OH) 2 in alkaline solution. Calcium is quantitatively separated from Sr and more than 95% of Sr is recovered from a sample with as much as 50g of Ca and a Ca/Sr mole ratio of 250. A new procedure for the separation of Sr from Ba and Ra is also investigated, which is based on the difference in solubility of the chlorides of Sr, Ba and Ra in HCl media. In 9.5moll - 1 HCl or 7.5moll - 1 HCl-10% acetone media, >97% of Ba and Ra can be removed by Ba(Ra)Cl 2 precipitation, and >94% of Sr was recovered. In the determination of 9 0 Sr by measuring 9 0 Y, the separation of Ra and Ba can easily be carried out by precipitation of Ba and Ra as Ba(Ra)SO 4 , while Y can be quantitatively recovered in the solution. By this method, a further separation of 9 0 Y from radiostrontium can be completed. The new separation procedure has been successfully used for the determination of 9 0 Sr in samples with high Ca content, such as 45l of seawater and 200l of drinking water. The analytical quality of the results is comparable to that of the traditional method using fuming nitric acid and BaCrO 4 precipitation.