In order to study the effects of wild mustard competition and different levels of nitrogen on effective traits of wheat yield, this research was conducted in Ahvaz, south west of Iran. The study was consisted of a split plot experiment, on the basis of Randomized Complete Blocks Design with three replications. Different levels of nitrogen (90, 150 and 210 kgN.ha-1) were assigned in the main plots and the sub-plots consisted of four wild mustard densities (0, 5, 10 and 15 weed plant.m-2). Result of analysis of variance showed the effect of nitrogen treatments on number of tiller per m2, number of spikelet per spike, seed yield, wild mustard biomass, wheat and wild mustard nitrogen agronomic efficiency was significant at 5% probability level and on number of seed per spike was significant at 1% probability level. Also effect of weed density on all measured traits (instead 1000-seed weight) were significant. But interaction effect of treatments on all traits was non-significant. Weed density had negative effects on nitrogen agronomic efficiency of wheat and positive effects on nitrogen agronomic efficiency of wild mustard. Seed yield was decreased in 0, 5 and 10 wild mustard densities per area unit. In the control plots by increasing nitrogen application wheat seed yield increased, but in wild mustard plots, with increasing nitrogen application loss of weed on economical yield increased. Generally, it seems that, wild mustard densities should be considered in determining the amount of nitrogen application, although 150 kgN.ha-1 recommended. Manuscript profile