Abstract: A branched alga collected from the intertidal zone of the Yellow Sea was characterized based on morphological observations and molecular phylogenetic analyses. The species exhibits distinctive morphological characteristics: thalli are purplish red, cartilaginous with a mucilaginous texture; erect and compressed, reaching 10–20 cm in height and 2—6 mm in width, growing singly or gregariously, and branching dichotomously or irregularly. Lateral branches are sparse or absent, with basal proliferations; the region bearing lateral branchlets near the branch base is relatively short, whereas the distal portion of the branches lacks lateral branchlets and is elongated. The thallus is composed of a filamentous medulla and a cellular cortex at both surfaces. Both carpogonial branch ampullae and auxiliary cell ampullae conform to the typical Grateloupia-type (6cpb-5auxb). Cystocarps are spherical and scattered across the thallus surface; tetrasporangia are cruciately divided. Molecular phylogenetic analyses based on rbcL and COI gene sequencessupport the distinctiveness of this new species from other members of the genus Grateloupia. Based on morphological and molecular evidence, the alga is proposed as a new species, Grateloupia maidaoensis sp. nov. This study contributes to the documentation of species diversity and provides a theoretical basis for the conservation of marine red algal germplasm resources in China.