This study was designed to examine the antifungal activity of Lactobacillus Plantarum DSMZ 20191 on a variety of molds which normally contaminated the fish diet and my cause it`s deterioration and also affect it's shelf life. We used different concentration of the antifungal metabolites (1,2,3,4 and 5 ml/100g of the fish diets) to demonstrate it`s role in inhibition of fungal growth during storage of fish diets. According to our study Lb. plantarum DSMZ 20191exhibit high activity against Aspergillus sp. which contaminated animal fish diet especially at concentration of 5%, while in plant diet the antifungal activity against  Aspergillus sp., Fusarium sp. and Penicillum sp.was lower. Finally the activity against Aspergillus sp. and Fusarium sp.in mixed fish diet was moderate.In conclusion LAB can be used in biopreservation due to their antifungal activity against a variety of molds which contaminate different food and feed and can cause serious deterioration and this can eliminate the use of chemical preservatives.