In the present paper, we propose a new method using the voronoi tessellation and the stereology to evaluate the local damage state due to voids during ductile fracture process. The damage tensor component is calculated based on a representative unit cell obtained from distribution function of line segments of voronoi polygons. Perforated sheets were set up as the plane models of damaged materials and were examined under the condition of uniaxial tension, where the deformation of circular holes is measured. The experimental results show that the distribution of damage tensor components obtained here corresponds well to the fracture pattern of model specimens. It is also shown that the local plastic deformation, i.e. the deformation of each hole is closely related to the damage tensor.