This research was carried out to investigate allelopathic effect of Peganum harmala on seed germination of Bromus tectorum. Aboveground and underground tissues of Peganum harmala in addition to its seeds were collected from Bijar rangelands. Collected materials of root, leaves, stem, seeds and a complex of mentioned parts were dried and powder. The research was performed at the greenhouse condition. The treatments included 1, 3, 6, 9 and 12 weight percentage of above mentioned powders. Also a control treatment was used, too. A completely randomized design (CRD) was applied for 4 weeks. Germination seeds were counted and recorded daily. Germination properties included: germination percentage, mean germination time, germination speed, inhibitory percentage. At the end of study period, radicle and stem length were measured. Data were analyzed by ANOVA. The results revealed that allelopathic effect of P. harmala resulted in negative effects on germination properties of Bromus tectorum. The high concentration of P. harmala has strong Allelochemicals inhibitory effects on germination and initial growth characteristics of B. tectorum. It was found that the materials obtained from different tissues of P. harmala had different levels of inhibition on germination properties of B. tectorum, so that seeds were the most inhibitor tissues. The lowest germination percentage and seedling growth resulted from 12g powder of seeds
