Alfalfa is one of the most important crops that are infested by Sitona species in Iran. Adults and larvae of Sitona spp. feed on foliage and root of legumes and cause serious damages on them. Collection of adults of this genus during 2003-2004 years from alfalfa fields of eleven localities in East Azarbaidjan Province, Sitona puncticollis Stephens was found to be the dominant species. To estimate of damage of this species, 100 pots of common alfalfa cultivar (Ghara yonje) were sowed and after 2.5 months. Fifty pots were infested with eggs of S. puncticollis and the rests were maintained as control. After two months, length of stem and roots and their dry and fresh weights were measured in 30 infested and 30 uninfested pots. The data of infested and uninfested pots were compared by T- test. Results showed that there were significant differences (P<0.01) between all measured traits in infested and uninfested pots.