The aim of this study was to investigate the effect of irrigation period on the quality and quantity of yield and some morphological and physiological traits of three multigerm sugar beet genotypes named BP Mashhad, BP Karaj and 191. The experiment was in a split plot based on randomized complete block design , carried out at Motahari Research station of Sugar beet Seed Research Institute in Kamalabad , Karaj in 2005. The main plots consisted of three irrigation periods, non-stress, medium stress and sever stress (80, 130 and 180 mm evaporation from class A pan , respectively) and the sub plots consisted of three genotypes. Irrigation treatments were applied at 6-8 leaf stage. The amount of irrigated water in each treatment was measured by WSC flom. Based on the results, the mean root yield of each treatment was 37.97(non-stress), 17.78(medium stress) and 15.46 (severe stress) ton/ha, and dry root weight of each treatment was 850 (non-stress) , 459(medium stress) and 15.46 (severe stress) g/m2. All the factors used affected yield, leaf area index , dry root and shoot weight in severe stress condition compared to the non-stress condition . The severe stress condition decreased root yield but increased sugar contents. Drought stress also decreased other measured traits such as root dry weight, total dry weight and leaf area index. Two genotypes BP Mashhad and BP Karaj were evaluated as drought tolerant genotypes.