Three cases of melanomatic neuroectodermal tumor of infancy(MNTI) were studied.The tumor mainly consisted of small neuroblastic-like cells and pigmented large cuboidal cell,and infiltrated adjacent tissues.The main ultrastructural charactristics were the presence of some membranebound dense-core secretory granules,numerous free ribosomes and polysomes aggregaed in rosettes,occasional mitoses in the small cells;and four types of membranebound pigment granules corresponding to melanosomes at different stages of maturation in the pigment cell.immunohistochemical results indicated that both of main cells were positive reaction for NSE,negative for S-100.These facts suggested they are immature in and malignancy.Further,the isogenesis of the tumor cells and embryo optic cup cells were discussed.