This study was performed on adult canines. After expansion of 1—3 days the skin was analysised with image-analysis-system, and its ultrastructures were observed with electronic microscopy.Results were: (1)There was no obvious changes of the thickness of the skin during the three days after expansion; (2)At the summit and middle of the skin from expansion of 1—2 days, the fibroblasts were enlarged increased in number, and more mitochondria and rough endoplasmic reticulums were found in the cytoplasm; (3) Succinate dehydrogenase(SDH)and the coiiagenous fibers were obviously increased at the summit and middle of the skin after expansion of 1-2 days (Plt;0.05), but SDH became weak and the coiiagenous fibers were decreased on the third day ,and (4) It was also found that the elastic fibers were decreased at the summit and middle the skin after expansion on 1-2 days,and at the middle and the periphery of the skin on the thirt day.