A field experiment was conducted at a field located in Ramadi city/ Al-Anbar province during the growing seasons of 2010 and 2011, to evaluate the potential variations in growth traits of some soybean cultivars and its role in determining of competitive ability of these cultivars to accompanied weeds and their inpact on yield and yield components.. The study involved four different weed treatments (weedy, weed free,Treflan EC45% herbicide spray at recommended concentration(1.152 g.ha-1)and half of recommended concentration, respectively) as main treatments, whereas, sub plots involved two plant densities which were (400000 plants.ha-1) and (266666 plants.ha-1). Sub-sub plots comprised of four soybean cultivars (Ls 75, Lee 74, Giza 111 and Giza 35).For soybean cultivars, Giza 111 characterized with its ability to reduced weeds density and its dry weights, and increased control percentage of the accompanied weeds in a degree better than other cultivars under study. This cultivar achieved higher mean values for no. of pods (86.58 and 92.51 pod. plant -1), 100 seed weight (14.39 and 14.27 g) for both seasons, respectively. This was positively reflected in total yield characterizing this cultivar by showing higher means (3.422 and 4.085 t. ha-1). This gave an indicator that this cultivar had an ability to tolerate weed competition comparing with Ls 75 cultivar which recorded the lowest means for most studied traits. Most of soybean cultivars showed a response to the different treatments of weed control higher than their response to plant densities in reducing accompanied weed density. However, weed density significantly decreased in the highest crop density (D1) comparing with lowest density (D2) during the period 90 days in both seasons. The density ( D1) gave highest seeds yield ( 3.66 , 4.26 t. ha-1).