Abstract: During macroalgae investigation, a new Grateloupia species from Wenchang, Hainan Province, South China, was discovered and named Grateloupia boaoensis Wang et Luan sp. nov. By using morphological observation and molecular analysis, we determined that G. boaoensis was purplish red, cartilaginous and slippery in texture, 15-40 cm high, with completely compressed and foliated axes with lateral branches and sword-shaped apex. The transverse sections were 400-800 祄 thick consisting of 4-9 layers of cortex cells and solid medulla, and the medullar filaments were longitudinal and intertwined. The new species exhibited typical Grateloupia-type auxiliary cell ampullae. Cystocarps were densely distributed on both axes and lateral branches. The four G. boaoensis sequences in this study were identical and formed a single monophyletic subclade with G. yinggehaiensis embedded in the Grateloupia clade based on ribulose-1, 5-bisphosphate carboxylase/oxygenase gene (rbcL) sequences. G. boaoensis was considered most closely related to G. yinggehaiensis by morphological observation and molecular analysis.