This experiment was conducted in order to study the effect of water deficit on some physiological characteristics,yield and yield components of two soybean varieties.Experiment were carried out in experimental field of Islamic Azad University-Karaj Branch and Tarbiat moalem university in 2004.In this research possibility of using mannitol for selection of soybean varieties during germination were exmined.Root and shoot lenght as well as germination and thier stability were measured then evaluated with factorial design under complete randomized design(CRD)with four replication.First factor was two varieties and second factor was four osmotic potential(0,-4,-8,-12 bar).Results showed significant differences(%1)between osmotic potential and varieties for root,shoot length and germination.In field experiment a split-split plot design under randomized complete block design(RCBD)with four replication were used.Varieties were factor A(Williams,Harcor)and time of selenium spraying(vegitative growth,begining of flowering was factor B and C was selenium concentration(Se=0,Se1=16gr/ha,Se2=21gr/ha).In field experiment fallowing characters were studied:seed yield,total dry weight,HI,seed 1000 weight,number of pods per plant,number of seeds per pod,chllorophyl a,b,relative water content,LAI,SLW,leaf cell membrane stability and antioxidant enzymes activity(superoxide dismutase,catalase and glutathione peroxidase).Results of field experiments showed that seed yield,total dry weight,seed 1000 weight,number of pods per plant,number of seeds per pod,SLA,SLW and LAI had significant differences,but others did not showed any significant differences.Results of irrigation treatments in combined analysis showed significant differences for all the characters.There was a logical relationship between characters measured in laboratory and some characters measured in field experiment.Williams variety that had longer root and higher root lenght stability than Harcor variety indicated better physiological and agronomical characteristics in field.Results of biochemical studies showed that antioxidant enzymes activity under drought stress and maximum activity of glutathion peroxidase obtained under using 21gr/ha selenium in Williams variety.