Disclosed is an improved process for the preparation of a new heteropolysaccharide by a fermentation process comprising culturing a heteropolysaccharide-producing strain of a microorganism of the genus Methylomonas on an aqueous culture medium containing methanol as the sole source of assimilable carbon. The concentration of the product polysaccharide in the fermentation broth is increased, the fermentation time is shortened, and the properties of the polysaccharide are improved by the controlled addition of methanol to the fermentation process near the end of the logarithmic phase of growth of the bacteria.