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In order to investigate the effects of seed density on grain filling process of barley genotypes, a factorial experiment was conducted in a randomized complete block design by using three genotypes of barley (Ezeh, Dopar Mahali and wi2291) and five seed densities (100, 200, 300, 400 and 500 grain m2) during cropping year 2006–2007 in agricultural research station of KhorrmAbad. To estimate grain growth factors, after pollination during eight samples taken at intervals of five days, the dry weight of one grain was measured. The results showed that the spike weight with number of spike m-2 (r= -0.82**) and filling rate with duration of grain filling (r= -0.78**) had a highly significant and negative correlation. The correlation between grain filling rate and grain yield was negative and highly significant (r= -0.44**) and non-significant correlation between the duration of grain filling and grain yield. Grain yield with biological yield, harvest index, hectoliter weight and spike number m2 had significant and positive correlation and significant and negative correlation with grain filling rate. Changes trend of single grain dry weight of the three genotypes of barley showed the highest dry weight of one grain was related to density 100 grain m2 and the minimum weight of the single grain of the mentioned genotype was related to density 400 grain m2. Seed genotypes filling rate between 1.213 to 1.333 mg per day and the different seed densities between 1.321 to 1.161 mg per day and for interaction between genotype and density between 1.070 to 1.620 mg per day ranged. Genotypes grain filling period between 33.72 to 38.72 days and for different seed densities between 32.70 to 39.94 days and for the interaction between genotype and density between 29.20 to 45.38 days ranged. It seems that in areas with climates with the final drought season stress, using varieties with higher grain filling rate are preferred.