Bromus kopetdaghensis is one of perennial plants of Poaceae family and it is important in biodiversity of arid and semi arid grasslands of Iran. This experiment was conducted as a completely randomized design with 4 replications in laboratory of faculty of Agriculture, Ferdowsi University of Mashhad, Iran.Treatments were different constant temperature of 5, 10, 15, 20, 25, 30, 35, and 40°C with 4 replications and in each replication 25 seeds were used. The results showed significant effects on different germination features of Bromus kopetdaghensis. The lowest germination rate (with 2.26 seed per day) was obtained at 5°C and the highest (with 11.39 seed per day) at 30°C. The maximum and minimum length of caulicle was obtained at 35°C (with 9.41cm) and 10°C (with 2.48cm), respectively. Maximum length of radical was also observed at 35°C (with 9.62cm) and minimum length of radical was observed at 10 and 20°C, without significant different with 3.63 and 3.48 cm. Based on the regression analysis between rate of germination and temperature the cardinal temperature of maximum, optimum, and minimum were obtained in the range of 0.71-4.25, 24-30.36 and 41.01-45.48, respectively.