Abstract: Ultrastructure changes of the skin lesions in three cases of malignant acantliosis aigricans were observed by SEM and TEM. Under SEM, the horap cells were irrgularly arranged in upturn and partially overlapped. On section tliere were papillomatosis and hyperkeratosis in the epidermis. Under TEM there were a large number of melanosomes, mainly stage Ⅲ and Ⅳ, is the dentritic processes of melonocytes. In the cytoplasm of phagocytes, many granules were observed, which were melanosomes or prelysosomes. These observations suggest that acanthosis aigricans has evidence of ultrastructural change.