Abstract:The present study reports the ultrastructural features of the vegetative cells in Jaoa bullata (Jao), Fan., an endemic species of Chlorophyta in China. Its thallus is composed of 3 layers of cells. Outer cells are the smallest in size, containing abundant cytoplasm, rich in various organelles; their vacuoles are smaller. The cells of mid-layer possess a large central vacuole. Their cytoplasm becomes a thin layer appressed against the cell wall; Various kinds of the organelles are still clearly visible. Inner ceils are extremely vacuolated. Their cytoplasm looks like degenerated. The cells are uninucleate, each containing a parietal, laminate chloroplast with numerous pores, which cause chloroplast a net-like appearance. The photosynthetic lamellae in a chloroplast include a number of thylakoids mainly in pairs. Chloroplast contains several pyrenoids, which are penetrated by 1 or 2 thylakoids. The present study deals with the structural characteristics of the mitochondria, plastids, endoplasmic reticulum and dictyosomes in the cells of Jaoa bullata. Two groups of intranuclear microtubules are present in a cell. Based on the similarity to Ulva mutabilis in the thylakoid arrangement and the ultrastructural features of the pyrenoids, authors suggest that daoa bullata (Jao) Fan may be closely related to Ulvaceae, among the advanced taxa in the evolution of Chlorophyta.