Objectives: Hygienic production and prevention of any kind of contamination is one of the most important principles of producing cheese. This study was carried out in the UF cheese factory with the 21 tones daily production, for the following goals: Rate of fungal contamination. b) The type of fungal contamination c) The source of contamination. d) To suggest effective methods of preventing fungal contamination.Methods: To estimate the prevalence of cheese contamination (Cl 95%) , 180 samples were selected and cultured after 53 days. The sampling was repeated 3 times in both warm and cold seasons. The fungal was then identified by studying the characteristics of the colonies and staining the microscopical structures. To determine the sources of contamination, the production line was also examined at the following points. a) Row milk. b) Milk passing through the second bactofuge. c) Milk passing through the pasteurization . d) condensed and pasteurized milk. e) cultured reservoirs. Results: The plates, waxy papers, aluminum foils and additives used in cheese production examined for possible contamination. Air contamination of the different parts of the factory was investigated by precipitation and filtration. The overall rate of cheese fungal contamination in 3 periods were 71%,55% and 48% respectively with and average of 60%. The most prevalent type of contaminant was the Penicillium spp. with the rate of 31% followed by A.niger (3.3%), Cladosporium (2.77%), Fusarium (2.6%), Alternaria (2.2%) and Paecilomyces (1.3%). The other fungi were observed in less than 1% of the cases. The raw milk to the factory was 100% contaminated. This rate reached zero after pasteurization. Th rates of contamination of the additives were as follows: rennet 16.6%, antifoam (5.5%), antiseptic (5.5%), thermopile (11.68), mesophile (0%) and salt (0%). The plates, papers, aluminum foils and water showed fungal contamination rates of 4.3%, 8.27%,7.6% and 5.5% respectively. The air was 100% contaminated with Penicillium spp.Conclusion: In spite of malti-factorial sources of contamination the factory air is the most important factor because the air was 100%contaminated with Penicillium spp. We concluded Penicillium spp .were the most prevalent type of cheese fungal contamination. Since the use of chemicals in dairy products is prohibited, it is suggested to utilize physical methods.