Abstract: The paper reports the observation on the deep dermis of the skin lesions from 10 patients with PSS by TEM. The collagen fibrils of PSS patients was thinner than that of normal adults (P<0.01), there was no significant difference between the fibrils of PSS patients and those of fetus (P>0.05). The fibroblasts of the PSS patients had plenty of cell organnelle and thin filiform substance. Collagen fibrils in different diameters and increased ground substance were observed in the specimen from a patient with rapid development in a short time. The observation on the skin lesions from 4 patients by SEM supported the above result. The collagen fibrils of the skin lesions from the PSS patients had the morphologic characteristic of the fetus collagen fibrils. It suggests that the fibrils are newly synthesiszed young collagen.