Many communities in the world use groundwater as a source of potable water. High nitrate concentration is a serious problem in groundwater usage. This study utilizes a biological denitrification method to investigate a moving bed biofilm reactor (MBBR) for the case of Tehran's groundwater. One pilot-scale MBBR was designed and used in this research with 3-liter volume. The denitrification reactor operates under anoxic conditions. Methanol was used as a carbon source in the reactor throughout the study, and fifty percent of the reactor volume was occupied with KMT packing (k1). To determine the optimum nitrate loading rate, the concentration of nitrate changed from 100 to 400 mg N/l. It was concluded that heterotrophic denitrifying bacteria converted nitrate to nitrogen. According to obtained results, the removal efficiency and optimum loading rate were estimated during the experiments in different concentrations and different HRTs for this type of reactor. Sodium nitrate was in the feed source in the anoxic reactor. The maximum nitrate removal rate was measured to be 2.8 g NO3-N m-2 carrier d-1. Therefore, it was shown that the optimum nitrate loading rate and the optimum COD/N were equal to 3.2 g NO3-N m-2 carrier d-1 and 6 g COD/g N, respectively.