Effect of plant oils against damping-off, and root rots of peanut compared to a recommended fungicide Rizolex-T was evaluated, under greenhouse and field conditions. Effect of four plant oils; cumin, thyme, garlic and cardamom at five concentrations (0.25%, 0.50%, 1%, 2% and 4%), on the linear growth of F. solani, M. phaseolina, R. solani and S. rolfsii. were tested. Garlic oil had the strongest and most extensive inhibitory effect on all fungi tested followed by thyme oil. Reduction in linear growth increased by increasing concentration of the tested plant oil from 0.25% up to 4%. Extended greenhouse and field trails for two successive seasons 2011 and 2012 proved that the application of essential oils significantly reduced peanut damping-off and root rots incidence. Thyme followed by cumin at 4% gave the highest effective on reducing damping-off and root rot incidence as well as increasing of percentage of survival plants. An opposite relationship between the disease incidence and concentrations of applied essential oils was recorded. The increase in peanut yield also followed the same trend. Data clearly proved that, ability of some tested plant oils to show relative similarly efficiency in reducing damping-off and peanut root rot incidence compared with the fungicide Rizolex-T. In this respect, thyme (4%) was the nearest one to the fungicides efficiency in reducing peanut pre- and post-emergence damping-off and peanut root rot incidence followed by cumin at the same concentration compared to other tested plant oils during greenhouse and field trials for two cultivation seasons 2011 and 2012.