Background: Sulfated polysaccharides have specific antiviral activities, which biological mechanism is assumed to the electrostatic interaction between (+)-charged virus surface glycoproteins and (-)-charged sulfate groups. Objective: For the elucidation of the mechanism, several oligopeptides referenced by the sequence of Human Immunodeficiency Virus glycoprotein 120 (HIV gp120) and hemagglutinin (HA) of influenza A and B were synthesized by a peptide synthesizer and the interaction with structurally distinct sulfated polysaccharides such as curdlan sulfate and dextran sulfate was analyzed by SPR. Method: In this study, six oligopeptides were synthesized from the sequence of the V3 loop, C-terminus, and CD4 binding domain in the HIV gp120. Oligopeptide A from the V3 loop comprises 20 amino acids with seven positively charged lysine and arginine in the sequence. The basic amino acids were relatively dispersed along the sequence compared with that of oligopeptide B. Likewise, oligopeptide B from the C–terminus comprises seven lysine and arginine, also oligopeptide of Influenza A/Yamagata HA and Influenza A/Brisbane HA comprises 23 amino acids with eight positively charged lysine and arginine in the sequence. Oligopeptide C from the CD4 binding domain and Influenza B /Hong Kong from the HA comprises one lysine and next to the biotin. The biotinylated peptides were synthesized by a microwave assisted solid phase peptide synthesizer using Fmoc protected amino acids. The peptides were purified by RP-HPLC and identified the structure by using MALDI TOF MS. Result: Peptides A and B from HIV gp120 were found to have interacted strongly with dextran and curdlan sulfates, however, the peptide C without positively charged amino acids showed no interaction. These results suggest that the interaction was due to the electrostatic interaction between negatively charged sulfate groups and positively charged amino groups of the peptides. The results of influenza HAs, influenza A (Yamagata and Brisbane) and B (Hong Kong) viruses, are also presented. Conclusion Curdlan and dextran sulfates were found to increase the interaction with increasing the molecular weights and degree of sulfation (DS), which were found to be important factors for the antiviral activity of sulfated polysaccharides. Based on the above, suggesting the antivirus mechanism of sulfated polysaccharides to be the electrostatic interaction of negatively charged sulfated polysaccharides and virus surface glycoprotein at the positively charged amino acid regions.