Water-soluble polyuronic acid was prepared via Acetobacter xylinum in this study. The structural features of the two polyuronic acid samples were characterized by gel permeation chromatography, Fourier transform infrared (FTIR) spectroscopy, and proton nuclear magnetic resonance (1H-NMR) spectroscopy. It was found that when using glucuronic or galacturonic acid as a substrate, with samples incubated at 20 °C to 30 °C in the fermentation medium for 3 weeks to 6 weeks, water-soluble polyuronic acid products could be collected from the colloids that formed on the surface of the medium. The yield of polyuronic acid was approximately 25 wt.%. The weight-average molecular weight of the product was 150,000 to 390,000, and the polydispersity was approximately 1.01 to 1.35. These results indicated that polyuronic acid can be easily prepared by a polymerization method using Acetobacter xylinum. The product polymers possessed high water solubility. The FTIR and 1H-NMR spectra indicated glycosidic linkages were successfully formed.