In order to evaluate, the effects of atrazin”s antitranspiration on yield four varieties potatos ( Ramos, Diamond,Santana, Agria) in adequate and limited moisture conditions. An experiment was conducted in azad university”s filed kerman branch in 2003. A split plot layout within a randomized complete blook desigin with three replications was used. of irrigation period (7,10 days) As main plot and sub plot with atrazin”s concentration of (0,100,150 ppm)was tested. The parameters of length stem,total number of tuber, total weight of tuber under study had significant and meaningless results for the three varieties (Ramos, Diamond, Santana) for irrigation period of 10days, and density of 150 ppm, in comparision with control of 7days irrigation period to zero density. But on agria variety,the test with variety of atrazin”s densities use on the stem”s length was meaningful and significant. Key Words: potato , Atrazin , stem's length , Total number of tubers , Total weight of tubers.