Astringency and sourness are two often confused sensations elicited by various compounds common in foods. The present study examined the effects of organic and inorganic acids on the astringency and sourness of aluminum sulfate and several types of tannins. Acids themselves were found to exhibit both sourness and astringency. Solutions containing an acid and aluminum sulfate were found to be less astringent than either the acid solution or the aluminum sulfate solution but were more sour than either solution alone. Solutions of acid and tannin were generally found to be both more astringent and more sour than either solute alone. The decrease in astringency of acid and aluminum sulfate solutions appears to be due to the chelation of aluminum ions by the acids used in this study. Increases in astringency of tannins when in acid solutions may be caused by decreased interaction of tannin with salivary proteins due to their protonation at lower pH.