Abstract: In order to investigate the effect of nitrogen fertilizer on biological yield of Balm(Melissa officinalis L.) an experiment was conducted under greenhouse condition at Research Institute of Forests and Rangelands Karaj/ Iran in 2004. The research was carried out with 6 levels of nitrogen fertilizer with 60, 90, 120, 150 and 180 kg N/ha and control ( without nitrogen). Statistical design was completely randomized design. Units of 15 pots were used per treatment. The nitrogen amount of the levels was added in 3 equal portions to the soil of pots. Results showed that effect of different levels of nitrogen on biological yield was significant in 90 kgN/ha treatment with 135.8 g dry weight per plant. Average production relative to other treatments had a significant difference. Reduction of yield at levels 120, 150 and 180 kg/ ha could be explained by the Mitcherlich law. High application in chemical fertilizer demolishes soil physical, chemical and biological properties. The optimal application of chemical fertilizers in plant production is a suitable approach in sustainable agriculture. Also results showed that highest essential oil percentage and highest essential yield respectively with .25% and 16.05 kg essence/ha were related to the 60kg N/ha treatment which were significant different from the control. Keywords: Balm(Melissa officinalis L.), nitrogen fertilizer, biological yield, essential oil