Barley is one of the most important cereal crops cu ltivated in the world and Egypt that is extremely d rought tolerant, making it an excellent choice for arid an d dry areas. However, quality and production is th reatened by major barley diseases as net blotch caused by (Pyre nophora teres), powdery mildew caused by (Blumeria graminis f.sp. hordei), leaf rust (Puccinia hodei) and Scald (Rhynchosporium secalis). A field experiment was c onducted to evaluate the use of Blue-green Cyanobacteria - O. agardhi i for integrated disease management of barley aga inst foliar pathogens and yield related traits in two lo cations as semi-arid land (Sinai) and normal con ditions (Giza) and two varieties (Giza 123 and Giza 133). Seeds an d foliar application of Blue-green Cyanobacteria O scillatoria agardhi i showed significant effective net blotch , powdery mildew , rust and spot blotch management. Blue-gre en Algae applied treatments increased antioxidant enzy mes as catalase (CAT), peroxidase (POD) and superox ide dismutase (SOD), as well as grain yield, kernel w eight in most cases and improved barley yield quali ty parameters and grain protein.