Abstract: Jaoaceae is an endemic group in China.The thallus of Jaoa is disc-shaped and with more or less uneven surface.The algae always live on the rocks in clean mountain streams.This family includes one genus——Jaoa,and two species: J.prasina and J. bullata.The criterion of dividing two species is the number of cell layers.J.prasina has two layers cells,while J. bullata has three layers cells in vertical-section.This paper reported the cellular structure of the genus collected from different regions in China under the microscopy,and measured the diameter of cells in each layer,and then described the protuberance structure on the cell of surface layer.Furthermore,we observed the ultrastructure of J. bullata collected from Xiuwu County,Henan Province.The feature of mitochondria with longitudinal arrangement tubular cristae of the alga is the warrant consideration.