Proteoglycans (PGs), which are present at animal cell surfaces and in the extracellular matrices, are involved in various biological events. PG consists of 1 or more sulfated glycosaminoglycan chains linked with a core protein, and a heparan sulfate-PG, syndecan is involved in the initial step of HIV-1 infection to the CD4+ lymphocytes and macrophages. Based on the structures of natural PGs, we synthesized new conjugated compounds that simulate macromolecular structure of PG, by combination of various types of unsulfated glycans and a core polypeptide, and named them as “Pseudoproteoglycans” (pseudoPGs). A pseudoPG synthesized by coupling 10 kDa poly-L-lysine (PLL) with 10 kDa dextran (Dex) exhibited remarkable anti-HIV-1 activity, which is more effective against R5 virus than sulfated polysaccharides, although neither PLL nor Dex has such an activity. Here we show the concept of the pseudoPG and the biological data focusing on the antiviral effects of the related compounds, to discuss the structure-activity relationship of the antiviral conjugates.