Wheat is the most important cereal crop, a staple food for more than one third of population world. Recently, there is increased interest in naturally produced active compounds as alternatives of fungicide and improve plant stress. Blue-green algae (cyanobacteria) secondary metabolites have a diverse antagonistic activity that lead to  disintegration of microbial growth and improve plant  resistant against stress.  So, this study was conducted to evaluate the antifungal activities of Oscillatoria   agardhii in retarding the growth of  wheat  pathogenic fungal species and improve resistance to biotic and abiotic stress under stress  conditions  in compared to the natural environment. Based on zone of inhibition formation and Minimal Inhibitory Concentrations (MIC), it was concluded that the extracts of O. agardhii  had significant antifungal and antimicrobial efficacy. Experiment was conducted under natural conditions at farmer’s field in middle of Sinai which saline soil and compared in a natural farm which a normal soil  to study the effective use of O. agardhii, resulted  in a significantly greater decrease in the  diseases incidence of powdery mildew, leaf rust and leaf spots, increased  of total soluble protein , proline,  soluble carbohydrates, Chlorophyll , carotenoids  NPK, K/N ratio  in wheat as well as plant growth and yield. The significant increase in grain yield of wheat was observed.  Cyanobacteria can be excellent biocontrol sources for plant pathogenic fungi as they can be easily cultured, less expensive compared to synthetic fungicides and ecofriendly, rather they can also promote plant growth. The investigation, certainly points out the necessity of exploring cyanobacterial strains as potentially outstanding sources of antifungal drugs,  Biostimulants and anti-stress that  improve plant resistance to abiotic stress.