The effect of eight organic acids (propionic, acetic, formic, lactic, tartaric, citric, oxalic and malic acids) as antifungal agents on the growth of four fungi (Aspergillus flavus, Penicillium purpurogenum, Rhizopus nigricans and Fusarium oxysporum) were studied. The high acidity appeared for oxalic acid being 0.14 at the high concentration (10%), while the lowest acidity recorded for propionic acid and acetic acid being 2.71 and 2.56 at the low concentration (5%). It was observed that, there was no relationship between the efficacy of organic acid and its final pH. Acetic acid (10%) has the highest inhibitory effect on A. flavus being 45.21%, but tartaric acid (5%) and citric acid (5%) gave the same lowest inhibition effect (0.42%). The lowest value of mycelium dry weight (MDW) of P. purpurogenum was 5.92 g/l when acetic acid was used (10%), but the highest value was 9.38 g/l when tartaric acid (5%) was used. Formic acid (10%) had a strong effect on the inhibition growth of R. nigricans being 28.65%, similar to propionic acid (10%), acetic acid (10%), lactic acid (10%), tartaric acid (10%) and citric acid (10%) being 26.57%, 26.38%, 26.19%, 23.53% and 24.48%, respectively. But malic acid (5%) and oxalic acid (5%) were having a week effect on R. nigricans being 5.31% and 6.45%, respectively. Lactic acid (10%) has the highest inhibitory effect on F. oxysporum being 34.45% and the lowest value was in the case of tartaric acid (5%) being 1.68%. Four treatments were used to determine aflatoxin B1 production. The highest inhibition (50%) was observed by R. nigricans in the presence of formic acid (10%). Acetic acid in 10% level inhibited the toxic secretion of A. flavus and P. purpurogenum to become 25% and 40%, respectively. Lactic acid (10%) gave 35% inhibition of toxin production in the presence of F. oxysporum.