The development of a method to mask bitter taste has widely been required in pharmaceutical science and food science. We found that a lipoprotein (PA-LG) composed of phosphatidic acid (PA) and β-lactoglobulin (LG) inhibits, selectively and reversibly, the frog taste nerve responses and human taste sensation to various bitter substances without affecting sweetness, saltiness and sourness. It was suggested that PA is a key material for the inhibition of bitterness because PA-containing lipoproteins show inhibitory action irrespective of species of proteins. As for the mechanism of bitter suppression, PA-LG would appear to mask the receptor site for bitterness on taste receptor membrane. Inhibitory action for bitterness by PA itself without protein was also examined in human. The result showed that PA selectively inhibits bitterness. The masking ability of PA for bitterness was satisfactory in practical use, although it was less than that of PA-LG. PA has been already in use as a masking additive for bitter taste of drugs and foods.