Abstract: In order to investigate solid and fluid nitrogen effect on biological yield and morphological characteristics of Balm (Melissa officinalis L.) an experiment was conducted in a field of Research Institute of Forests and Rangelands, Karaj/ Iran in 2004. The research was carried out with 2 levels of 4.5 and 6 percent of fluid nitrogen on plant and 2 levels of 60 and 90 kg N /ha in the soil, and with control (without nitrogen) for comparison. Nitrogen levels were applied with 3 equal portions. The statistical design was completely randomized block design with 4 replications. Results showed that effects of different rates of nitrogen application on biological yield, root length and root weight, height, tiller number and stem diameter were significant (%1) and leaf width was significant (%5) too. The comparison of average production showed that highest biological yield with 8099 kg/ ha was related to the 60 kg N / ha treatment which was significant different from control treatment. The compared of average root length and root weight showed that highest root length and highest root weight respectively with 43.63 cm and 75.6 g/m2 were related to the 90 kg N/ ha treatment which were significant different from the control. Application of nitrogen spraying was significant on biological yield relative to control but the production of spraying method reduced .Yield reduction at levels 90 kg N/ha in soil and 6 percent nitrogen spraying on plants was explained by Mitcherlich Law. Also effects of different rates of nitrogen application on internodes and lateral stem were not significant (%5).The comparison of average characteristics showed that highest height (76.83cm) and highest tiller number (51.07) were related to the 90 kg N/ ha treatment, which were significant different from the control. The comparison of average leaf width and stem diameter showed that highest leaf width and highest stem diameter with 5.30cm and 3.67 mm respectively were related to the 4.5 % spry of nitrogen on plants and 60 kg N/ ha in the soil treatments which were significant different from the control. Key words:(Melissa officinalis L.).nitrogen, morphological characteristics, biological yield.