In this research, the effect of drought stress on antioxidant enzymes, membrane stability and essential OIL PERCENTAGE in Balm (Melissa officinalis L.) has been evaluted under field conditions. Experimental design was complete randomized block design with 4 replications. The treatments included: T1 (control, non stress), T2 (80%FC), T3 (60%FC), T4 (40%FC) and T5 (20%FC). Results showed that there was a significant differences (P<0.01) between treatments on evaluated traits such as catalase, nitrate reductase, peroxides, membrane stability and PERCENTAGE of essential OIL. The mean comparison of treatments showed that amount of product catalase content that produced in T5 (%20FC) with 31.09 mmol decayed H2O2 per second was higher than other treatments. It was also well defined that nitrate reductase in T4 (40%FC) with the mean of 3.543 mmol produced nitrate per fresh weight, was higher than other treatments. There was not any significant differences between T4 and T5 for their peroxidase contents but they had higher peroxidase that other treatments. Mean comparisons of membrane stability between treatments, showed that in moderate stress condition, the membrane stability increased in comparison with control treatment but in treatments with higher drought stress, the membrane stability has been decreased. The PERCENTAGE of essential OILs of collected samples from natural rangelands of Tehran, Ardebil and Esfahan provinces was compared with cultivated plants in the field. Results of analysis variance of collected plants from natural rangeland showed a significant differences between treatments for plant height, stem diameter and PERCENTAGE of essential OIL at %5 probability level. The mean comparison showed that samples collected from Ardebil with %0.3961 essential OIL, Esfehan with 36.60 cm plant height and Ardebil with 2.867 mm stem diameter were superior over other treatments. It could be concluded that Balm has a high adaptation to different climatic condition.