The title compound (C29H50O2, Mr = 430.69) was isolated from the algae Halimeda xishaensis collected from the South China Sea. Its crystal structure was determined by single-crystal X-ray diffraction for the first time. The crystal belongs to orthorhombic, space group P212121 with a = 8.1560(13), b = 10.7861(18), c = 29.973(5) ? V = 2636.8(8) 3, Z = 4, Dc = 1.085 g/cm3, F(000) = 960, (Mo-K? = 4.533 mm-1, ?= 0.71073 ? S = 1.061, (?max = 0.382 and (?min = 0.244 e/?. The structure was refined to R = 0.0561 and wR = 0.1553 for 2711 observed reflections with I > 2(I). X-ray diffraction analysis reveals that the title compound has two ?OH groups, and the side chain is saturated. There exist two intermolecular hydrogen bonds between three molecules. The crystal compound was (C29H50O2, Mr = 430.69) was isolated from the algae Halimeda xishaensis collected from the South China Sea. Its crystal structure was determined by single-crystal X-ray diffraction for the first time. The crystal belongs to orthorhombic, space group P212121 with a = 8.1560 (13), b = 10.7861 (18), c = 29.973 (5)? ​​V = 2636.8 (8) 3, Z = 4, Dc = 1.085 g / cm3, F (000) = 960, Mo-K = 4.533 mm-1,? = 0.71073? S = 1.061,? Max = 0.382 and (? Min = 0.244 e / ?. The structure was refined to R = 0.0561 and wR = 0.1553 for 2711 observed reflections with I> 2 (I). X-ray diffraction analysis reveals that the title compound has two? OH groups, and the side chain is saturated. There exist two intermolecular hydrogen bonds between three molecules.