Lavendula officinalis plants were grown in perlite substrate culture, treated with three nicotinamide concentrations (0, 75 and 100 mg/L), also foliar spray with two different irrigation scheduling (10, 15 times/day) were used. Essential oil (extracted from two cuts) composition was identified using gas chromatography (GC). Essential oil samples were tested for their antimicrobial activity against five Gram positive bacteria, five Gram negative bacteria, six fungi, and four yeasts. The antimicrobial potency was determined by measuring the inhibition zone (mm) using whole plat diffusion technique. GC data showed the superiority of 1,8 cineol which varied from one cut to another according to the rate of irrigation and application of nicotinamide. Linalool was the second major constituent in all treatments; it showed vacillation due to nicotinamide application and the rate of irrigation from one cut to another. Antimicrobial inhibitory effect of most of the resultant lavender essential oils increased with increasing their volume from 2 to 5 µl. Most strains of fungi and Gram positive and negative bacteria showed high sensitivity and were inhibited to a great extent. Different strains of yeast showed high resistance and survived essential oils test. Data clearly indicated the marked inhibitory effect of lavender crude oil samples against several human and plant pathogens and non pathogenic micro organisms.