Abstract: Development of sporangium at the early stage and the differentiation of plastids in Dryopteris erythrosora were studied using light microscopy and transmission electron microscopy.Results showed that:(1) The development of Dryopteris erythrosora sporangia belonged to the leptosporangiate type.(2) The tapetum was mixed type, with an inner amoeboid tapetum layer, and outer parietal tapetum layer.(3) The plastids in the initial cell of the sporangium differentiated in three ways.First, the plastids containing starch grains in the initial cells were allocated into the lower cells and then the cells of the sporangium stalk.Second, the newly formed plastids in the initial sporangium cells were allocated into the upper cells and then into primordium cells, except the apical cells.The plastids with starch grains in the apical cells were allocated into the initial cells of the sporangium wall.Third, the plastids with starch grains in the apical cells were also allocated into the internal cells of the young sporangium.The internal cell divided periclinally and formed sporogenous cells and tapetal initial cells, both of which contained newly produced plastids.The sporogenous cells and the spore mother cells contained the plastids with starch grains.The spore mother cells also contained oil bodies.The young spores possessed amyloplasts and oil bodies.Both the inner and outer tapetum cells possessed newly formed plastids.With the degeneration of the tapetum, the amyloplasts occurred in the outer layer of the tapetum cells and oil bodies occurred in the inner layer of the tapetum cells.(4) The differentiation of the plastids in Dryopteris erythrosora was similar to that of microspore development in some angiosperms.The present investigation provides new cytological features for the differentiation of plastids in different tissues during sporangium development.It also lays a foundation for studying the developmental biology and phylogeny of ferns.