Halogens are known to be accumulated in all kinds of marine algae and through halogen peroxidases, chloride, bromine and iodine can be assimilated as organic compounds by the same mechanism (Vilter, 1984; soedjdak et al., 1990) Although a number of bromine-containing organic compounds are found in various red algae (e. g. Blackman et al., 1982; Weinstein, 1975; Chantraine et al., 1973; Pedersen et al., 1974; Craigie et al., 1967), it has not still been well studied in brown algae, as shown by the very few reports on this subject(Koch et al., 1982). The metabolic role and physiological importance of the bromine-containing compounds in seaweeds is poorly understood, although there were some speculations on these compounds’ antialgal, antibacterial and growth promotion activities (Pedersen et al., 1974; Nisizawa et al., 1979). Attention was recently paid on the role of volatile organic bromine compounds playing their potential effects on the upper atmosphere and environment (Muosmaa et al., 1990). The bromo-compounds in marine algae should be under further investigated to elucidate the production pathway and ecological cycle of bromine in the excreta and huge biomass of marine algae. In this paper, describes a new method, guided by X-ray analytical microscope to fractionate and isolate the organic bromine compounds in Sargassum fusiformis, is described.