The extracts from Ulva lactuca have biological and nutritional values. The protein was 48.7 mg/g dry wt, soluble carbohydrate 43.9 mg/g dry wt, insoluble carbohydrate was 223 mg/g dry wt and lipid was 18.3 mg/g dry wt. Maximum antifungal activities of U. lactuca were observed with ulvan extract. The most predominant fungi in spoiled tomato sauce cans were Aspergillus flavus (33.6%), Rhizopus stolonifer (26.8%), and Fusarium oxysporium (22.3%). The minimal fungicidal inhibition concentration of ulvan extract against A. flavus and R. stolonifer were 10 mM and 15 mM, respectively. The colony deactivation of A. flavus and R. stolonifer by ulvan extract occurred was 91% and 89%, respectively, at 25 C after 72 h, but the deactivation occurred at 100% after 24 h at 4°C. Results affirmed the damaging effect on both tested fungal spores' walls and intercellular components. So, ulvan polysaccharide can be used as a natural preservative for raw or processed tomato sauce to increase its shelf life.