Abstract: Analysis of the dermo-epidermal surface in three-dimensions is important for evaluating cosmetics. One approach is based on the active contour model,which is used for extracting local object boundaries with closed curve form. The dermo-epidermal surface,however,is a plane with open form. Developed in this paper is a method of automatically extracting the dermo-epidermal surface from volumetric confocal microscopic images,as well as constructing a 3-D visual model of the surface by using the geometric information contained in the control points. This method is a 3-D extension of the active contour model,so it is called active open surface model （AOSM）. The initial surface for AOSM is an open curve plane,guided by a 3-D internal force,a 3-D external constraint force,and a 3-D image force,which pull it toward the objective surface. The proposed technique has been applied to extract actual dermo-epidermal surface in the given volumetric confocal microscopic images.