PROBLEM TO BE SOLVED: To provide a leaf or extract of purple basil preserved in a state where anthocyanin coloring matter originating from the purple basil is concentrated. SOLUTION: A method for treating the purple basil comprises (1) a step of adding table salt to the leaf of the purple basil, (2) a step of dehydrating the leaf of the purple basil obtained in the step (1), and (3) a step of soaking the leaf of the purple basil obtained in the step (2) in the solution of an organic acid. In the step (2), a sufficient physical effect for destroying a cell is given to the leaf of the purple basil to be dehydrated or a physical effect of the degree which does not destroy the cell is given to the leaf. COPYRIGHT: (C)2004,JPO