During recent years, turf grasses are cultivated as a prominent component of landscapes and as sport fields in Iran. Several studies were conducted on etiology of some important diseases of cool season grasses, which causes high losses in different parts of Iran. Cool season grasses are the main turf grasses which are generally cultivated in Iran and they are belonged to the Pooideae family including Agrostis tenuis, Festuca rubra, Lolium perenne and Poa pratensis. Bipolaris, Curvularia, Drechslera and Exserohilum diseases of turf grass are concerned in this study. Bipolar is and Exserohilum diseases caused irregular brownish green to black leaf lesions. The stem and leaf sheath lesions were purple to black purple, and an extensive rot of stems, crowns and root may be occurred. Infected plants became chlorotic and then brown. The severe cases resulted in a severe thinning of turf. Exserohilum rostratum (Drechs) Leonard & Suggs, B. hawaiiensis (Ellis) Uchida & Aragakai, B. sorokiniana (Sacc.) Shoem and Bipolaris spicifera (Bainer) Subram. were isolated from infected grasses which were found pathogenic on turf grass. Curvularia species caused general decline and tip die back on turf grasses, crown and leaf sheath infections resulted in dark brown dry rots, Curvularia lunata (Wakker) Boedijn and C. ovoidea (Hiroe & Watan.) Muntanola were isolated from infected plants, C. lunata isolate was found pathogen on turf grass. Drechslera poae (Baudys) Shoemaker and D. dictyoides (Drechs) Shoemaker caused leaf spot, root, crown, and rhizome rot, wilting and chlorosis, followed by dead and browning on Lolium perenne and Poa pratensis.