Abstract: Photometric method is used to determinate aluminum in high pure bismuth trioxide. Bismuth disturbance is eliminated by volatilizing bismuth bromide with hydrobromic acid after the test sample is dissolved in nitric acid. Aluminum in the solution reacts with chrome azurol S to form a stable tribasic complex in a buffer solution (pH 6.7) of acetic acid and acetate ammoni um in the presence of octylphenol polyoxyethylene ether. The maximum absorbance is 620 nm with an apparent molar absorptivity of 2.30×10⁵ L/(mol·cm). Beer's law is obeyed in the concentration range of 0～10 μg/50 mL of aluminum. The method has been satisfactorily applied to the determination of trace aluminum in high pure bismuth oxide.