To study the effects of applied nitrogen levels and wild mustard densities on the growth of wheat and wild mustard, a field experiment was conducted at Re-search and Experimental Field of Islamic Azad University of Ahvaz-Iran. The effects of three nitrogen levels namely 90, 150 and 210 kg.ha-1 and four wild mustard densities such as 0, 5, 10 and 15 plants.m-2 were evaluated in split plot arrangement with randomized complete block design in three replications. The results indicated that in weed free plots the spike length, plant height, harvest index and grain yield of wheat increased with increasing nitrogen application from 90 to 210 kg.ha-1 by 11.4, 10, 3.7 and 12.5 % respectively, while in the presence of wild mustard these parameters were decreased. Increasing nitrogen level increased the competitive ability of wild mustard and increased loss of wheat grain yield. The results also indicated that the biomass of wild mustard increased by increasing nitrogen level and wild mustard density. The biomass of wild mustard was 108.7, 157.2 and 226.6 g.m-2 under 90, 150 and 210 kg.ha-1 N, respectively. Manuscript profile