Abstract: It is an object of the present invention to find substances that can be used as skin aging markers, and the present invention provides a method for determining the degree of skin aging, including measurement of expression of secretory proteins and/or intracellular proteins and/or their genes in skin cells and/or skin tissues, wherein the secretory proteins and/or intracellular proteins change their expression with aging of skin. The present invention also provides a kit for determining the degree of skin aging and a method for identifying substances effective in the prevention of skin aging.