Field experiments were carried out under natural infection of basil downy mildew in the Experimental Farm of Sids Horticultural Research Station, Agric. Res. Center, Beni-Sweif governorate during 2016 and 2017 growing seasons in order to evaluate the efficacy of different irrigation intervals and interplant spacing levels on basil downy mildew epidemic caused by Peronospora belbahrii and productivity of basil plant. In general, irrigation intervals and interplant spacing levels significantly affect the disease incidence and severity as well as basil growth parameters (plant height, no. of branches, fresh and dry weights of herb, oil ratio and essential oil yields) at the end of the experiment. The high efficacy was obtained from plots irrigated at 12 day interval and planted at 20 cm spacing. Although, those irrigated at 16 day interval and planted at 25 cm spacing gave the highest reduction in disease incidence and severity but drastically affected plant growth and oil yield to the lowest value.