Crop production is challenged in our world by increasing food demands, decrease natural resource bases and climatic change. Nowadays plant growth regulators works like fertilizers in increasing plant growth production efficiency and needed to produce in large industrial scale. Fermentation condition and medium constituents can significantly affect on the product production and designing an acceptable fermentation medium is critical importance. In this paper Fusarium sp. could be considered as promising indole-3-acetic acid producers with the ability to improve the production using statistical methods. The results showed that fermentation type, incubation temperature and L-tryptophan were the most influencing parameters on the production. Maximum IAA production by Fusarium oxysporum was 300.4 mg/l obtained under the fermentation conditions: temperature at 25oC, incubation period 5 days, pH 7, inoculums size 2%, shaking rate at 150 rpm and medium constituents: Glucose 40 g/l, yeast extract 3 g/l, L-tryptophan 1 g/l, KH2PO4 2 g/l, NaNO3 4 g/l, MgSO4·7H2O 0.1 g/l with regression analysis (R2) 99.67% and 2.12-fold increase in comparison to the production of the original level (142 mg/l).