Abstract: In order to find out the economic species and biomass of dominant species of marine macroalgae on intertidal areas of ten islands in Guangdong Province, and to provide references for the conservation and development of economic marine macroalgae and construction of marine ranching in Guangdong Province, we conducted a survey on 46 stations of these islands by qualitative and quantitative methods from January 2021 to February 2023. The results show that a total of 55 species of economic marine macroalgae including 14 species of Chlorophyta, 30 species of Rhodophyta and 11 species of Phaeophyta were collected from these ten islands. Sargassum hemiphyllum and Corallina pilulifera were the main dominant species. The highest biomass of S. hemiphyllum was 40.72–55.25 kg·m⁻² and that of C. pilulifera was 4.32 kg·m⁻². G. furcata and G. tenax, whose biomass decreased significantly, were no longer the dominant species in these islands. The results demonstrate that the resource status of dominant species of economic microalgae in Guangdong islands has undergone significant changes. It is needed to protect the economic species of macroalgae whose resources have decreased significantly.