Abstract: Experiments have been designed to determine the effect of growth substances, which included Indole Butyric Acid (IBA), Gibbrellic acid (GA3), Ethrel and Paclobutrazol (PBZ) at 50, 100 and 150 ppm in minimizing the damage of Alternaria alternata in faba bean compared to Tridex-80% fungicide. In vitro, results revealed that all concentration of PBZ and high Ethrel concentrate (150 ppm) completely inhibited the linear growth of Alternaria alternata. In vivo, all growth substances at any concentration reduced significantly severity and incidence of Alternaria leaf spot disease. The maximum reduction was recorded with PBZ followed by Ethrel. All photosynthetic pigments significantly increased by IBA, Ethrel and PBZ treatments. PBZ was more effective followed by Ethrel. Whilest, GA3 and Tridex-80% decreased chlorophylls a and b. Total phenols and total soluble carbohydrates are reached to the maximum values when using Ethrel followed by PBZ. Plant height was increased significantly with growth promoter (IBA and GA3), GA3 was the most effective. On the other side, using of growth retardants (Ethrel and PBZ) increased significantly number of branches/plant, paclobutrazol (PBZ) came first. Yield components (pods number/plant and weight of 100 seed) increased significantly with any level of growth substances. The maximum values occurred under Ethrel followed by PBZ. This research clearly showed that there is no significant difference between the efficacy of growth substances (Ethrel and PBZ "at 150 ppm") and fungicide tridex-80% in reducing Alternaria leaf spot disease of faba bean plant.