Five cyanophyte species (Amorphonostoc punctiforme, Gloeocapsa turgidus, Sphaeronostoc coeruleum, Stratonostoc linckia f. spongiaeforme and Synechococcus cedrorum) were isolated and identified from sandy Egyptian soils. Polysaccharides extracted from these species showed a pronounced antiviral activity against Rabies and Herpes-1 viruses represented by the absence of the characteristic cytopathic effects of these viruses. It was found that 100 μg polysaccharide/ml induced 100% inhibition of the two viruses which, depending on the polysaccharide concentration. Both of Gloeocapsa turgidus and Synechococcus cedrorum showed higher antiviral activity against rabies virus than that against herpes-1 virus. Amorphonostoc punctiforme showed nil to weak antiviral activity against both viruses. It was suggested that polysaccharides of such species of cyanophyte react against human and animal viruses. So, it could be concluded that there is a need for further studies to explain the mode of action of these substances on the replication of different viral origins to know how one deals with cyanophyte polysaccharides as antiviral substances in the most suitable and effective manner.