Cyanobacteria are one from the main classes of bacteria that promote growth of plants and in biocontrol of soil-borne fungi. In vitro and in vivo, this study investigated the effect of application Nostoc spp. filtrates (Nostoc lichenoides, Nostoc indistinguendun and Nostoc favosum) on the Fusarium oxysporum and Rhizoctonia solani that infects cotton (Gossypium barbadense L.) plant. Nostoc spp. strains were tested to antagonize both pathogenic fungi. Total phenolic compounds, polysaccharides contents and dry weight were determined of Nostoc spp. strains. In a greenhouse test in soil infested with F. oxysporum and R. solani isolates the three filtrates from cyanobacterial strains and their mixture were effective in increasing the dry weight and the surviving seedlings percentage; however, the filtrates of strains had no effect on seedling height. The strains showed that the highest efficiency to inhibit the post-damping off of F. oxysporum and R. solani when they were applied in a mixture. Under field conditions the three strains were consistently effective in increasing stand and yield of cotton plant in 2021 and 2022 growing seasons; however, their efficiency was much higher when they were applied in a mixture. Finally, from the obtained data we concluded that using biotic factors for controlling damping off of cotton plant pathogens such as F. oxysporum and R. solani were effective.