Abstract: A process for purifying aromatic polycarboxylic acid produced by liquid phase catalytic oxidation of polyalkyl aromatic hydrocarbon to remove undesirable aldehyde aromatic carboxylic acid and other impurities including the step of contacting an aqueous solution of said impure acid and hydrogen with a noble metal-containing catalyst, our improvement comprising eliminating any gas phase during the contacting step and conducting said contacting step with said aqueous solution by maintaining hydrogen at about 10 to about 75 percent of saturation in the liquid reaction medium to produce purified aromatic polycarboxylic acid having delta Y values below ten.