A method for developing an excellent material for enhancing skin barrier function, and providing a cosmetic which is developed based on the method and has excellent ability to enhance skin barrier function is described. The method evaluates skin barrier function by the steps of 1) culturing normal human epidermal cells in wells having a semipermeable membrane with two sides, in presence and absence of a test substance; 2) adding a medium not containing metal ions to a first side of the semipermeable membrane in each well and a medium containing the metal ions to a second side of the semipermeable membrane in each well, provided that the cells are adhered to the first side of the semipermeable membrane; 3) culturing the cells; 4) measuring the concentration of the metal ions in each medium; and 5) calculating permeability of the metal ions in the epidermal cell layer based on the measured concentrations of the metal ions in each media. The test substance is effective for enhancing skin barrier function when the permeability is reduced in the medium in which the test substance is added compared to the permeability in the medium in which no test substance is added. The larger the level of reduced permeability, the higher the suitability of the test substance as a material for enhancing skin barrier function.