To investigate the relationship between the structure of curdlan sulfate with beta-[1-->3]-D-glucan as main chain and the anti-HN activity, three regioselective substituted curdlan sulfates (CS’s), i.e., CS having sulfate groups at all C6 and some C2 positions (62S), CS having sulfate groups at all C4 and some C2 positions (42S), and CS having sulfate groups at some C6, C4, and C2 positions (642S), were synthesized. Their structures were characterized by C-13 NMR spectroscopy. These curdlan sulfates had number average molecular weights in the range 6.2 x 10(3) to 10.8 x 10(3). For the various curdlan sulfates, anti-HIV activities and anticoagulant activities were assayed in vitro. It was revealed that these curdlan sulfates showed high anti-HIV activities in the EC50 range 0.04-0.4 mu g/mL when the degree of sulfation was more than 1.3, and low cytotoxicities as well as low blood anticoagulant activities. Furthermore, it was found that the anti-HIV activity of curdlan sulfates depended on the degree of sulfation but not on the position of sulfate groups.