Greenhouse and field studies were conducted in 2009 and 2010 to study the effect of growth regulators, which included Indole Butyric acid (IBA), Gibbrellic acid (GA3) at 50, 100 and 200 ppm Ethylene (Et) at 0.1%, 0.2%, and 0.4%, in reducing of peanut damping-off, wilt and root rot diseases. All tested growth regulators clearly affected on the incidence of damping-off, wilt and root rot disease, under greenhouse and field conditions Indole Butyric acid (IBA) at 200 ppm followed by Ethylene (Et) at 0.4% were the most effective treatments in reducing peanut infections with damping-off, wilt and root rot, while treatment with Gibbrellic acid (GA3) at 200 ppm recorded the highest infection compared to other treatments. There were positive relationship between increasing the concentration of IBA and Et and their effect on incidence of damping-off, wilt and peanut root rot, while with GA3 this relationship was negatively. Results of the present study indicated that treatment with growth regulators like many of inducer resistance factors was associated with specific biochemical defense reactions. Among these biochemical changes the increase in phenol contents (free, conjugate, & total phenols) and the increase in oxidative enzyme activity (peroxidase, polyphenoloxidase and catalase).