Hyperbranched polyester/graphene oxide (HPES/GO) is prepared by in-situ polymerization technique to ensure complete homogeneity of GO in the formed composite. Chemical structure of the composite is studied using FTIR and its thermal stability is investigated by TGA. The prepared composite is used as active filler for cellulosic paper through additions of different ratios during sheets-making. Physical and mechanical properties beside thermal stability of the paper sheets have been examined. The results showed that both density and thermal stability of loaded paper are increased while porosity is decreased significantly with increasing amount of filer. However, the paper sheets demonstrated very low water permeability when loaded with 20% PES/GO. Paper sheets dipped for 1 min. in flaxseed-gel showed improved water vapor permeability compared with uncoated sheets. Moreover, the loaded sheets acquired significant antibacterial activity against different microorganisms. This property is declined upon coating with flax seed gel but still higher than blank sheets.