Culture supernatant fluids (SF) of mutant 108 obtained from Streptococcus sobrinus 6715, when incubated with sucrose, produce large amounts of water-soluble glucans. Mainly, two water-soluble glucan synthesizing glucosyltransferases (GTases) were found in culture SF by isoelectric focusing. These two GTases had higher activities than those from the parent strain. The GTase which synthesizes water-insoluble glucan totally lacked the mutant. When the glucan preparation synthesized by the SF was subjected to gel filtration, a major large molecular weight fraction (designated glucan A) and a small molecular weight fraction (designated glucan B) were obtained. Glucan A yielded a smaller molecular weight glucan after treatment with dextranase. Glucan B was not hydrolyzed by the same enzyme.