Disclosed is a kaempferol preparing method comprising isolating kaempferol from kaempferol glucosides using an acid, a base, an enzyme or a microbe producing the enzyme. More specifically, the method comprises obtaining a plant extract containing kaempferol glycosides from a plant using water or an organic solvent; and hydrolyzing the plant extract using an acid, a base, an enzyme or a microbe producing the enzyme to isolate kaempferol. The kaempferol glycosides comprise camelliaside A or camelliaside B. The plant extract is derived from a seed or leaf of green tea. When using the method of the invention, it is possible to mass- produce kaempferol, which is one of main physiological activating ingredients, from a plant, particularly a seed or leaf of green tea.