The present invention has objects to provide a glucan useful as water-soluble dietary fiber, its preparation and uses. The present invention solves the above objects by providing a branched ?glucan, which is constructed by glucose molecules and characterized by methylation analysis as follows : (1) Ratio of 2, 3, 6-trimethyl-1, 4, 5-triacetyl-glucitol to 2, 3, 4-trimethyl-1, 5, 6-triacetyl-glucitol is in the range of 1 : 0.6 to 1 : 4; (2) Total content of 2, 3, 6-trimethyl-1, 4, 5-triacetyl-glucitol and 2, 3, 4-trimethyl-1, 5, 6-triacetyl-glucitol is 60% or higher in the partially methylated glucitol acetates; (3) Content of 2, 4, 6-trimethyl-1, 3, 5-triacetyl-glucitol is 0.5% or higher but less than 10% in the partially methylated glucitol acetates; and (4) Content of 2, 4-dimethyl-1, 3, 5, 6-tetraacetyl-glucitol is 0.5% or higher in the partially methylated glucitol acetates; a novel ?glucosyltransferase which forms the branched ?glucan, processes for producing them, and their uses.