To study seed dormancy and the after-ripening period in barley genotypes (57 Dutch genotypes and two Iranian cultivars (Gorgan and Valfair)), an experiment of randomized complete block design (two replications) was conducted at the Research Farm of Collage of Agriculture and Natural Resources, University of Tehran in 2004-2005. In the growing stage of ZGS92, panicle was collected. The percentage of seed dormancy and germination were assessed at 20?c in three replications. Among the 57 genotypes, 38 had a low percentage of germination (dormant) while the rest (21) were non-dormant. The control cultivars exhibited a high level of dormancy and low percentage of germination. To evaluate the duration period of dormancy in seeds, test of after-ripening was conducted on the dormant genotypes and on control cultivars for a duration of five weeks (three replications). The length of after-ripening on water uptake rate was studied. For seed water uptake experiment Gorgan and CGN00962 genotypes were selected. The effect of dormant seed coat extract and dormant embryo extract on percentage of germination, length of coleoptile and length of radicle in the non-dormant seeds were investigated. Finally the superficial changes in the seed coat after the period of after-ripening were investigated with the aid of an electron microscope. The results revealed that there existed significant genetic variations for seed dormancy and the duration length of after-ripeining among genotypes. This will facilitate selection for these traits among genotypes. During after-ripening, germination and water uptake increased. The results of seed extract showed that percentage of germination, length of coleoptile and length of radicle, in non-dormant seeds, decreased when non-dormant seeds placed in the extract solution of dormant seeds. The highest inhibition was observed when the non-dormant seeds put in the extract of dormant seeds' coats. The results of electron microscopic studies revealed that after-ripening brought about some changes in the seed coat. After having under gone the passing of this period, spiral threads were found as deleted and splits detected appearing on the seed coat.