To study the reaction of two rowed barley landraces from west of Iran, 278 accessions from eight provinces were planted in Karaj and Gorgan Station, in an observation trial without replication. Infection rate was measured using the method of Saari and Prescott. Some agro morphological characters such as grain yield, flowering date, plant height were also measured. Results showed that the accessions had different reactions to powdery mildew. The range of infection varied from O (immune) to 8 (susceptible) in Karaj, and from 2 (resistant) to 9 (very susceptible) in Gorgan. The frequencies of infection rates of 6 and 7 (moderately susceptible) were 38.4% and 39.2% in Karaj and Gorgan, respectively. Difference of means at two stations was significant (t = 2/04). The frequencies of resistance and moderately resistance reactions were 4.4% and 1.1 % in Karaj and Gorgan, respectively. Reaction to powdery mildew with other agronomic characters such as flowering date showed a negative and significant correlation.