The characteristics of the lactan gum produced by Rahnella aquatilis varied according to the carbon sources used : the steady shear viscosity of lactan gum produced from fructose medium was higher than that produced from the other carbon sources, and furthermore the level of energy required (Delta H), for the degradation of lactan gum from fructose by Rahnella aquatilis was higher than that from other carbon sources. The lactan gums produced from sucrose or lactose contained mannose, galactose and galacturonic acid in the approximate molar ratio of 5:3:2. However, the lactan gum produced from galactose, glucose or fructose contained the same sugars at 2:4:4, 2:3:5 and 7:1.5:1.5 respectively.