Sulfated alkyl malto-oligosaccharides with potent anti-human immunodeficiency virus (HIV) activities were synthesized. Malto-oligosaccharides composed of glucose residues of 4-7 were used as the starting materials. The synthesis of alkyl malto-oligosaccharides was carried out by reacting the peracetylated oligosaccharides with aliphatic alcohols by hetero-polyacids or Lewis acid as catalyst. After deacetylation, OH-free alkyl malto-oligosaccharides were sulfated with a sulfur trioxide-pyridine complex. Sulfated alkyl oligosaccharides in which the number of glucose residues ranged from 5 to 7 had potent anti-HIV activities comparable to the very strong activity of curdlan sulfate having the strongest activity of so-far synthesized sulfated polysaccharides. However, the tetraose derivatives had considerably low activities. The cytotoxicity was considerably high in the case of sulfated alkyl oligosaccharides with long alkyl groups such as an octadecyl group. The anticoagulant activity of almost all sulfated alkyl maltooligosaccharides was almost zero.