Fungal diseases of poultry have become problematic as bacterial and viral diseases. This study was designed to investigate the prevalence of fungal agents in broiler chickens and to detect the activity of carvacrol using agar dilution method against these isolates. Mycological examination was conducted on 227 broiler chickens` samples in El-Fayoum Governorate in the period from February 2015 to May 2016. Forty nine fungal isolates were recovered with a prevalence of 21.6% including 29 moulds (12.8%) and 20 yeasts (8.8%). Mould isolates were recognized as 5 A. fumigatus (2.2%), 6 A. flavus (2.6%), 10 A. niger (4.4%), 1 A. nidulans (0.4%), 1 Cladosporium (0.4%) and 4 Penicillium species (1.8%). All yeast isolates were recognized as Candida species. C. albicans was the most prevalent; 11 isolates (4.8%), followed by C. krusei; 4 isolates (1.8%), C. tropicalis; 3 isolates (1.3%), and C. glabrata; 2 isolates (0.9%). The antifungal activities of carvacrol against the recovered fungi revealed that carvacrol completely inhibited the growth of all tested fungal isolates at concentrations of 0.1, 0.25, 0.5, and 1% while a concentration of 0.01% has no effect on the fungal growth.