This paper presents the ultrastrticture of free--living filament cells of Porphayra haitanensis which were observed by scanning and perspective electronic microscope.There were clearly a number of ridges on the outside walls of free-living filament cells and. a pit-connection in the inner wall between two neighbouring cells.In the cytoplasm, there are two types of endoplasmic reticulations: the rough endoplasmic retirulation (RER) and the smooth endoplasmic reticulation(SER). They are distri-buted around tlza nucleus and near the cytoplasm membrane. It can be seen obviously that connected endoplasmic reticulations with the nuclear membrane. The nucleus is not always elliptical in intermittent fission stage but irregular. rI'here are some pores on the nuclear membrane. The thylolkoids, phycobilisomes, romasomes, floridean starch and ribosome were also observed.