Oligo-glucomannan (OGM) could be obtained through enzymolysis from KGM, a water-soluble polysaccharide isolated from Konjac flour. The sulfated derivative of OGM (OGMS) was prepared by chlorosulfonic acid method with formamide as a dehydration-condensation agent. OGMS was one kind of low molecular weight polysaccharide sulfate which had different weight-average molecular mass (Mw) ranging from 1.8 to 2.0 KDa and different degree of substitution (DS) ranging from 1.25 to 1.73. FT-IR and ¹³C NMR spectra indicated that the sulfated groups had been introduced at C-2 0C-6 and C-3 positions of OGMS. OGMS had significant inhibitory effect on the growth of HepG2 and Hela cells in vitro at concentration higher than 0.2mg/mL. On the other hand, OGMS was a potent inhibitor of viruses HBV, IAV and CBV₃, with IC₅₀ values determined in vitro of 8.3, 4.2 and 3.1µÀgmL^-1, respectively due to its sulfated groups and low molecular weight. The results showed that konjac oligo-glucomannan sulfate could be developed as a new type of medicine which had potential antiviral activity.