Abstract: An opening/closing apparatus of petals of artificial flowers adapted to unfold and fold petal members like a natural flower. The apparatus has an expansion member internally disposed underneath a body to expand during absorption of liquid or to shrink during evaporation of the liquid; a medium member disposed above the expansion member to upwardly move according to expanding force of the expansion member; a restoring member coupled to an upper side of the medium member to downwardly move the medium member according to resilience; and a plurality of petal members respectively hinged to periphery of the body, each at a predetermined height to unfold outwardly when the medium member descends or to fold inwardly when the medium member ascends.