Sulfated polysaccharides have been widely studied because the presence of sulfate groups are related to anticoagulant and antithrombotic activities, and also because their presence increases polysaccharide-water interaction, thereby lowering their viscosity. Botryosphaeran, an exopolysaccharide (EPS) of the 1,3;1,6-b-D-glucan type secreted by the ascomyceteous fungus, Botryosphaeria rhodina, when grown on glucose as sole carbon source, is part of an important class of polysaccharides that show biological and pharmacological activity. Besides that, the high viscosity of botryosphaeran exhibited in aqueous solution presents difficulties with the biological tests. In order to resolve this problem chemical derivatisation by sulfation was chosen to make the botryosphaeran more water-soluble and also to tailor new properties. Firstly, prior to sulfation, the purity of the material was determined by gel filtration chromatography, where the EPS eluted as a single symmetrical peak. Next, the EPS was solubilised in formamide and pyridine by vigorously stirring for 24 h, followed by the dropwise addition of chlorosulfonic acid over a 1 h period in an ice-bath. The mixture was then maintained at 4 ^oC for 15 h. Ice-water was then added to terminate the reaction, and the mixture neutralized with aqueous sodium bicarbonate until effervescence ceased. The solution was then dialyzed and lyophilysed. UV-VIS spectroscopy showed a new band at 259 nm, attributable to the transition of sulfate due to the unsaturated bond formed in the sulfation process. FT-IR spectra showed two new bands at 808 cm^-1 and 1244 cm^-1, indicating, respectively, a symmetrical C-O-S vibration associated with a C-O-SO₃ group, and an asymmetrical S=O stretching vibration. The degree of sulfation (DS) was determined according to Dodgson and Price (1962), and found to be 1.53. Following the methods described above, the botryosphaeran was highly sulfated and the resulting product showed low viscosity in aqueous solution.