Lactobacillus strains are used as probiotic bacteria in fermented dairy products and other fermented food products, whereas they are known to prolong the shelf life of these products. The inhibitory effect of cell free supernatant (CFS) of several Lactobacillus species on mycelium growth and the aflatoxin production by   the aflatoxigenic strain of Aspergillus parasiticus was studied. A complete inhibition (100%) of mycelium growth and aflatoxin production was recorded when cell free supernatant of Lactobacillus casei was placed in a dialysis sac or in the medium without a dialysis sac or on the insertion of A. parasiticus after 16 hours with L. casei. Both L. reuteri and L. gasseri inhibited mycelium growth and aflatoxin production but to a lesser extent.                 Cell free supernatant of L. acidophilus and L. bulgaricus showed the lowest effect on aflatoxin production as well as on mycelium growth. The inoculation of bacterial strains of L. casei, L. gasseri and L. reuteri before fungal growth inoculation by 16 hours caused inhibitory effects on mycelium growth and aflatoxin production. But these indications were not observed for the other treatments of L. acidophilus or L. bulgaricus.                 The probiotic strains (L. casei, L. reuteri) with higher antifungal activity were used and incorporated in the manufacture of Ras cheese to replace the normal starters (S. thermophilus, L. bulgaricus), where they prevented the growth of fungi during the three month of the storage period. In conclusion probiotic bacteria may be able to produce active substances that can inhibit aflatoxins production by A. parasiticus in most treatments used, and the inhibitory effect depends on the type of lactic acid and / or the treatment used.