The plant density has a direct influence on morphophysiology , yield components and yield of cowpea . In order to evaluate the behavior morfoagronomico a modern cultivar of cowpea [ Vigna unguiculata ( L. ) Walp . ] Under different plant densities , an experiment was conducted in the municipality of the Dawn Gurgueia -PI in irrigation system sprinkler in the agricultural year 2009/ 2010. We evaluated five populations of plants ( 100 , 200 , 300 , 400 and 500 000 plants ha-1 ) by randomized complete block design with four replications . The increase in population from 100 to 500 000 plants ha - 1 caused reductions of 30.19 % in stem diameter , 96.5 % in the number of branches , 63.8 % in the number of pods per plant and 67.6 % in grain yield per plant . The epicotyl length increased linearly with increasing plant population . The weight of hundred grains was not significantly influenced by different plant populations . The different plant densities promote significant changes in the morphology and yield components of cultivar