Effects of carbon sources on zooglan production by Zoogloea ramigera were investigated. The production of zooglan was varied according to the carbon sources used. The largest amount of zooglan was obtained when lactose was used as carbon source and fermentation broth with lactose showed the higher viscosity. The effects of carbon sources were in decreasing order of lactose, glucose, galactose and sucrose. The viscosities of purified zooglan solutions (5g/L) obtained from different carbon sources were measured. When lactose was used, the viscosities of zooglan solutions was quite high and other carbon sources such as glucose and galactose gave little lower viscosities than lactose but sucrose gave very low values. On the other hand, it could be postulated that most of lactose is hydrolyzed by intracellular ${eta}$-galactosidase.