Abstract: Based on the study of optimum conditions of the reaction system,a sensitive photometric method for determination of trace amount of aluminum was proposed.Aluminum(Ⅲ) was reacted with 2 mL of 500 mg·L-1 o-HPF solution in an ammoniacal buffer medium of pH 9.5 in the presence of 4 mL of 50 g·L-1 KF solution and 2 mL of the 50 g·L-1 Tween-20 solution.Fluoride ion was used as an auxilliary complexing agent for Al(Ⅲ) and Tween-20 was used both as solubilizer and sensitizer for the chromogenic reaction.Interferences of several common co-existing metal ions except Ti(Ⅵ) were eliminated by adding 4 mL of 20 g·L-1 EDTA solution after the addition of KF.Linearity between values of absorbance and mass concentration of Al(Ⅲ) was found in the range of 0 to 0.16 mg·L-1.Molar absorptivity (ε) of the multi-componental reaction system found was 1.5×105L·mol-1·cm-1 at the wavelength of absorption maximum 550 nm.The proposed method was applied to the determination of aluminum in samples of brass,magnesium alloy,potassium carbonate and waste water,giving RSD′s (n=5) less than 2.5%.