Phylloid algae are important reef-builders in the late Carboniferous.This paper focuses on the paleoecology of phylloid algae in the Late Carboniferous on well-exposed reefs in Ziyun County, Guizhou Province.Phylloid algae growing closely packed are attached via holdfast or similar structure to substrate.They were growing in environments such as shallow water,photic zone and below the wave base with medium energy currents.They have a variety of morphological forms,such as single cup-shaped,cabbage-shaped and clustering cup-shaped.The thalli are of certain tenacity and intensity.In the areas dominated by phylloid algae,other marine organisms are relatively scarce. Obviously,phylioid algae are stronger competitors for living space than other co-occurring organisms.