The exopolysaccharides produced by Z. ramigera mutants were purified by the precipitation with isopropyl alcohol and characterized. The physiological changes of mutant cells resulted the changes in the structure of the product, Zooglan, which could be determined by the measurement of hydrodynamic properties. Zooglans produced by Z. ramigera SL, SLR and MM1 gave intrinsic viscosities of 14.3 dl/g, 12.2 dl/g and 9.1 dl/g, respectively. The intrinsic viscosity of Zooglan produced by Z. ramigera MM1/pLEX2F increased to 14.8 dl/g. The hydrodynamic property expressed as the intrinsic viscosity of Zooglans could explain the alteration of the structure of Zooglan synthesized by the physiological activities of the mutant cells.