The spread of Saprolegnia fungus throughout the incubation period and the prohibition use of chemicals such as Malachite Green, necessitate the substitution of antifungal compounds with high efficiency and minimum environmental side effects. Garlic (Allium sativum) is a plant whose antifungal and antimicrobial properties have been frequently studied. Therefore, the aims of the present study were to assess the antifungal effects of aqueous, ethanol and methanol extracts of garlic on Saprolegnia fungus, determine its minimum inhibitory concentration for the fungus growth and compare the minimum inhibitory level of the garlic extracts with Malachite green and Bronopol. Saprolegnia fungus was isolated, purified and identified from the infected eggs. Ethanolic, methanolic and aqueous garlic extracts were prepared. The inhibitory effects of different concentrations (0.3, 0.5, 3, 50 and 100 mg/ ml) of these extracts were tested 48 hours after fungus growth using wells method. Results showed that inhibitory level of all tested extracts on the growth of Saprolegnia fungus at day (D) 1 and D2 was significantly different from D3. The ethanolic extract of the garlic with 3 mg/ml concentration showed the highest inhibitory effect on the Saprolegnia fungus growth rate compared to Malachite green and Bronopol. The level of MIC for aqueous, ethanolic and methanolic extract was obtained as 0.3 mg/ml.  Consequently, garlic extract possesses antifungal effects and it can be used as an antifungal in the aquaculture industry due to its herbal origin and having no side effects on aquatics and consumers.