Qualitative and quantitative determinations of uronic acids and uronides were carried out by conductometric and potentiometric titrations and paper chromatography.1. The dissociation of glucuronic acid lactone is very slow in neutral and acidic solutions. In titrating by Ba(OH)2 solution, pH increases rapidly and becomes alkaline before active dissociation of the lactone commences.On the other hand, uronic acids (acidic form) react immediately with Ba(OH)2 and completely turn to the barium uronates below pH7 (see Fig. 1). Therefore, the proportion of uronic acids and their lactones can be determined by combination of conductometric and potentiometric titrations.2. A paper chromatographic determination of uronic acids and their lactones in the presence of other sugars was carried out by means of multiple developments of their barium salts with n-bu-tanol-benzene-pyridine-water (10:2:5:5) and ethyl acetate-acetic acid-formic acid-water (18:3:1:4), followed by colorimetric determination of the uronic fractions separated clearly from the other neutral sugars.Uronides in gum arabic and pectin resist considerably against hydrolysis, but large amount of them were hydrolyzed to monomers by elongation of the secondary hydrolysis to 10_??_12hrs. (see Fig. 2 and Table. 1).Decomposition of uronic acids during acid hydrolysis was investigated(see Fig. 3 and 4), and then the uronic acid contents of gum arabic and pectin were determined by means of paper chromatography.The values of these uronides obtained by this method agreed closely with those obtained by the CO2 method.