It　has　been　revealed　that　numerous　nanoparticles　are　formed　during　the　boiling　preparation　of　traditional　Chinese　medical　decoctions　and　culinary　soups.　They　may　possess　physiological　effects　different　from　those　of　constituent　components　and　are　worth　paying　attention　to　but　are　barely　noticed　and　investigated　as　of　yet.　In　this　study,　six　groups　of　nanoparticles,　whose　size　ranged　from　57　to　300　nm,　were　successfully　isolated　from　the　decoction　of　Isatis　indigotica　Fort.　root,　according　to　their　particle　size　by　the　means　of　size-exclusive　chromatography.　All　of　the　obtained　nanoparticles　have　a　high　content　of　polysaccharides,　which　distinguishes　them　from　the　disclosed　BLG　protein　nanoparticles.　They　also　have　high　similarities　in　other　compositions,　surface　charge,　and　stimuli　responses.　However,　four　out　of　these　six　nanoparticles　(F2,　F3,　F4,　and　F5)　exhibited　significant　antiviral　activity　against　influenza　virus　H1N1,　and　their　antiviral　activities　and　cytotoxicity　towards　MDCK　cells　varied　with　their　sizes.　It　suggested　that　the　antiviral　efficacy　of　BLG　decoction　could　also　be　from　its　nanoparticles　besides　its　well-known　antiviral　phytochemicals.　It　also　implied　that　the　biological　effects　of　these　polysaccharide　nanoparticles,　including　cytotoxicity　and　antiviral　activity,　may　be　correlative　with　the　physicochemical　properties,　especially　the　particle　size.