An object of the present invention is to provide a method for eliminating the hydroxyl group at the 9-position of a urolithin to produce another kind of urolithin. This object is achieved by a method for producing a second urolithin, including Step (a): allowing, in a solution containing a first urolithin, a microorganism having an ability to produce the second urolithin from the first urolithin to produce the second urolithin from the first urolithin.
