The aim of this study was to quantify the response of Bromus tomentellus, Hordeum bulbosum and Agropyron trichophorum to continuous grazing of sheep in semi-arid rangelands of Lorestan. In two areas, grazed and ungrazed, 4 transects of 200 meters were established and 10 random points were selected along of each transect and at each point the nearest plant considered for further study. Morphological traits of each selected plant were measured i.e. height, internode distance, root length, root weight, production and mass. After reviewing the data normalization, the averages between grazed and ungrazed were compared by non-paired t-test. The effect of livestock grazing on height, shoot internode, length and root weight, biomass and yield of H. bulbosum and A. trichophorum were significant. The mean weight of H. bulbosum in the ungrazed and grazed areas was 117.1 gr and 16.1 gr, respectively, and the height of A. trichophorum was 525.1 mm in the ungrazed and 334.7 mm in the grazed areas, respectively. Grazing of livestock had no significant effect on the height and internode distance of B. tomentellus (p>0.05). Animal grazing significantly increased root length of 58.35 mm in B. tomentellus. In general, the results of this study showed that different species of plants exposed different reactions and trade-off against grazing depending on the type of plant species. Knowledge about of the morphological changes of plant species against grazing can greatly help us for the management of sustainable grazing in the rangelands.