Common cocklebur is considered a strong weed competitor to maize and distributed all over the world and Egypt. Knowledge about the nature of competition to maize is the key of planning weed management crop strategies in this crop. Then, the aim of this investigation was to determine the economic threshold of common cocklebur for maize. Where two field experiments was conducted in naturally heavily infested soil with common cocklebur at Mallawy Agriculture Research Station, Agriculture Research Centre, EL-Minia Governorate during 2014 and 2015 seasons. A split-split-plot design with three replicates was used. These experiments included three factors, main plot included two maize hybrids i.e, SC 166 ( Single cross 166) and SC 173 ( Single cross 173) , the sub plot three corn densities of 20000, 24000 and 30000 plants  feddan^-1 and the sub sub plot were randomly to common cocklebur densities of 0, 2, 4, 6 and 8 plants  m^-2. The main finding of this research show that sown SC173 was high competitive than SC 166 to common cocklebur and reduce its dry weight and gave highest yield and yield component of maize. Also, increasing maize density reduced in common cocklebur dry weight, ear length, ear weight, grains number ear^-1, 100- grain weight, plant height and LAI. Maize density at 24000 plant fed^-1 gave the highest grain yield (ard fed^-1) in both seasons compared to other maize densities. So, increasing common cocklebur density, decreased common cocklebur dry weight, maize grain yield and yield components such as plant height, leaf area index (LAI), ear length, ear weight, grains number ear^-1, 100- grain weight and grain yield of maize (ardab faddan^-1). Maize yield losses at 1, 4 and 8 common cocklebur plants  m^-2 reached to  5.2, 22.0 and 44.4 %, respectively, as  compared zero common cocklebur plants m^-2 in the first season and calculated from regression equation by 4.9, 21.0 and 42.5 %, respectively, in the second season. The main findings of this investigation refer that common cocklebur weed should be managed to avoid  maize grain yield losses due to its competition through growing maize vigor hybrid such as SC173 with proper plant density  at 24000 plant fed^-1 and continues hand pulling any emerged common cocklebur seedling or to use selective recommended herbicides.