The present invention provides dark opal basil leaves or an extract thereof, containing anthocyanin dye derived from the dark opal basil, in concentrated form.The process of the present invention comprises steps of (1) adding salt to dark opal basil leaves, (2) dehydrating the dark opal basil leaves obtained in step (1), and (3) immersing the dark opal basil leaves obtained in step (2) in an organic acid solution. In step (2), the dark opal basil leaves to be dehydrated are physically treated to such an extent that the cells thereof are broken or not broken.