Drought serves as one of the most important abiotics affecting crop growth and production. The main objective of the present study was to evaluate genetic variation and estimate of genetic parameters for forage yield, seed yield and associated traits in 25 half-sib families of Bromus inermis under two moisture environments (normal and drought conditions). High genetic variation was observed among the families for most of the studied traits. Results indicated that drought stress significantly affected all forage related traits and all seed related trait except for panicle length. Physiological traits were also affected and except for prolin they were all decreased under drought stress. At first harvest the highest phenotypic coefficient of variation under stressed condition was observed for number of ear per plant (84.46%) and for the second harvest under drought stress condition it was observed for number of ear per plant (89.22%). The highest broad sense heritabilities under normal (non-stress) and drought conditions were related to dry forage yield for second cut (93.54%) and dry forage yield for second cut ( 97.47), in the second harvest respectively. Narrow sense heritability for dry forage yield was 60% for non-stress and it was 46% for stress conditions. These values were 47 and 41% for seed yield , under the two conditions respectively. Based on dry forage yield genotypes 3, 5, 6, 8 and 23 and based on seed yield genotypes 14, 17, 21 and 23, showed higher general combining ability. Under non-stress condition, dry forage yield showed positive and significant correlation to chlorophyll a, b and total chlorophyll. Seed yield under non-stress condition showed negative and significant correlation with prolin content. According to regression analysis seed weight in panicle, seed number in panicle and seed number in panicle accounted for 81and 69% of seed yield variation. Path analysis for seed yield showed that under control condition, Panicle fertility and panicle length and under drought stress condition, seed number per Panicle and Panicle number per plant had the highest direct effect on seed yield. Results of factor analysis under both moisture conditions indicated that six hidden factors were accounting for more than 66% of total variation of all traits. Results of variance analysis on drought susceptibility and tolerance indices based on seed yield and in terms of dry forage yield there was significant variation for all indices, suggesting that these indices can be used to select tolerant genotypes. Based on principle component analysis of indices, first and second components were nominated as production potential and tolerance, and based on forage yield, they were nominated as forage yield and drought stress sensitivity respectively. Results of 3-D graphs for seed yield and dry forage yield separately and STI index showed that families 1, 3, 4, 6 , 7 , 10 , 14, 15, 21, 23 and 25 in respect to seed yield and families 3, 4, 6, 7, 10 and 15 in respect to forage yield were located at A area which can be used to improve yield under both stress and normal environments. Keywords : Bromus inermis , Half-sib families, genetic variation, drought stress