<;P>;PROBLEM TO BE SOLVED: To provide a masking agent capable of masking with the addition of an extremely small amount, rough taste of food and drink and drug, and flavor too strong as flavor of food and drink and drug, without changing the basic flavor balance of food and drink and drug, and to provide a masking method. <;P>;SOLUTION: This masking agent contains as the active ingredient, milk serum mineral which is obtained through the processes (a), (b) and (c) as follows: (a) a process of separating demineral liquid from milk or whey by membrane separation and/or ion exchange to obtain high mineral liquid (I); (b) a process of heat treating the high mineral liquid (I) to separate/remove calcium-phosphate complex and obtain high mineral liquid (II); and (c) a process of concentrating and/or drying the high mineral liquid (II) until to bring solid content to &ge;20 mass% so as to obtain milk serum mineral. <;P>;COPYRIGHT: (C)2008,JPO&INPIT