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. We have developed 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. Our method is a 3-D extension of the active contour model, so we call it the 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.