Such natural and nonnatural sugars as D- and L-glucoses and D- and L-mannoses were reacted with curdlan to form branched curdlans, respectively. These structures were analyzed by means of C-13 NMR spectroscopy and methylation analysis. The branched curdlans were sulfated with piperidine-N-sulfonic acid in DMSO to give branched curdlan sulfates. It was revealed that these branched sulfates had high anti-AIDS virus activities in the EC(50) range of 0.3-1.2 mu g/mL in vitro using MT-4 cells and exhibited low cytotoxicities as well as low anticoagulant activities. Furthermore, for L-glycosyl-branched curdlan sulfates, retention times in rat in vivo calculating from their anticoagulant activities were a few hours.