Abstract: We found that malonic acid is a specific masking agent for Al in complexometric titration, and by using the DCTA-malonic acid masking method, Al can be indirectly titrated. This paper reports that 3-100μg of Al (in 35 ml) can be accurately spectro-photometrically titrated with this method at pH 5.5 without the interference of the following metal ions: Zr, Th, Sn, Bi, Fe, Ti, Ga, Ce, La, Y, Gd, Cr, Hg, Cu, Ni, Co, Pb, Zn, Cd, Mn, V, Sb, Mo, W, Ca, Mg, etc. The selectivity of the titration is very high. When the Al is titrated at pH 3.5 less metal ions will not interfere, but it allows larger amount of Ca and Mg present.This method was successfully used to determine the microquantities of Al in limestone, dolomite, quartz and tap-waters.