Abstract: The colour reactions of barium (Ⅱ) and strontium (Ⅱ) with dibromomethyl carboxyazo were studied comparatively. In the medium of H₃PO₄, the colour reaction of barium (Ⅱ) is highly selectivity and tolerates the existence of 6-fold of strontium(Ⅱ). And in the buffer medium of H₃BO₃-Na₂B₄O₇,the absorbances of colour coordination compounds for barium(Ⅱ) and strontium(Ⅱ) have an additivity over a certain range of concentrtion.On these grounds, a new method of the successive determination for barium and strontium had been developed.