Abstract: A field experiment was carried out during two successive seasons at the Experimental Farm of the Faculty of Agriculture, Kafr El- Sheikh University to evaluate some essential oils as biocontrol agents for powdery mildew on Zinnia elegans, L. Marjoram, clove, cinnamon, garlic, ginger and fennel oil were used as a foliar spray at 2 levels (250 and 500 ppm) beside Kema zein 75% and distilled water as a control. The plants were sprayed four times beginning from June 15^th with one week interval by a hand atomizer as soon as the first sign of powdery mildew detected on plants. Disease incidence and severity as well as vegetative parameters such as plant height, number of branches per plant, leaf area, fresh and dry weights of shoots, root length and fresh and dry weights of roots were determined in the two seasons. Peroxidase and polyphenol oxidase activities were determined after 24 hour from the last spray in leaves samples. The highest significant decrease in disease incidence and severity and the best results for most of the studied growth and flowering parameters and total green colour were recorded when plants were sprayed with ginger, cinnamon and clove oils, respectively each at 500 ppm compared to the other treatments in both seasons. In addition, the activities of peroxidase (POX) and polyphenol oxidase (PPO) enzymes increased as a result of oil spray on plants. In conclusion, these findings provide a rational basis for possible utilization of these essential oils as a safe and alternative method to fungicides for controlling powdery mildew in zinnia plants.