A sulfated oligoglycoside acylate comprising monosaccharides of a single or two kinds as the constituents, wherein the hydrogen in the hydroxyl group at the 1-position of a reducing end sugar of the oligosaccharide formed via the glycoside bond of these monosaccharides has been substituted with an aglycon selected from a group consisting of alkyl groups, aromatic alkyl groups, aromatic alkoxy groups and tocopheryl groups; from 12 to 80% of the residual hydroxyl groups have been acylated with an acyl group selected from a group consisting of aliphatic acyl groups and aromatic acyl groups; and 88 to 20% thereof have been sulfated; or a physiologically acceptable salt thereof provided that compounds wherein the aglycon is an alkyl group and the acyl group is an aliphatic acyl group are excluded is disclosed. Further, an antiviral agent, which exerts a long-lasting antiviral action particularly on HIV, containing said compound as an active ingredient is disclosed.