Sainfoin ( Onobrychis .) is widely grown as forage and pasture legume in Iran and is tolerant to environmental stresses. With more than 170 annual and perennial species, it is an important forage and pasture legume originated from Iran and Anatolia. Despite wide geographical distribution in Iran, little information is available on genetic diversity of sainfoin accessions in seed related traits and their association with forage characteristics. In order to investigate the variation and relationship among seed yield and its components, 93 genotypes from 21 wild and cultivated species of genus Onobrychis were evaluated according to a randomized complete block design with four replications during 2013-2014 in Isfahan University of Technology Research Farm. The results indicated considerable variation between studied germplasm for all traits. Panicle fertility and seed yield per plant had the most phenotypic coefficient of variation in cultivated and wild genotypes, respectively. Panicle fertility and panicle length had the most genetic variation in cultivated and the wild genotypes, respectively. The highest broad sense heritability was estimated for one-hundred seed weight and panicle length in cultivated and the wild genotypes, respectively suggesting contribution of the major genes for controlling these traits. Among studied species, O. inermis showed highest seed yield and dry matter yield. O. montana and O. oxyodonta had highest fresh matter yield. Among species, O. vaginalis، O. chorassanica ، O. vassilczenkoi and O. sintenisii had the most resistance and O. persica had the most susceptibility to powdery mildew. Results of correlation analysis showed that seed yield was positively correlated with number of stem per plant, number of seeds per panicle and dry and fresh yield and negatively correlated with panicle length, days of 50 percent flowering and powdery mildew. In order to determine traits involved in accounting for seed yield variation, stepwise regression was undertaken. On the basis of stepwise regression analysis, number of stem per plant and number of seed per panicle justified the majority of seed yield variation. The result of path analysis indicated that number of stem per plant and number of seed per paniclehad the most direct and positive effect on seed yield. Results of clustering analysis based on morphological traits could segregate species based on genetic similarities. Key words : sainfoin, genetic diversity, wild species, Cluster analysis