Ten barley (Hordeum vulgare L.) genotypes, five lines originated from International Barley Germplasm Pool (IBGP) and (Nile valley Red Sea Regional Program (NVRSRP), International Center for Agricultural Research in the Dry Area (ICARDA), Aleppo, Syria, and the five commercial varieties, Giza 123, Giza 124, Giza 125, Giza 126 and Giza 2000 were evaluated for (Blumeria graminis f.sp. hordei) powdery mildew resistance. The genotypes were tested at the seedling stage with 16 differential isolates of Powdery mildew and at adult stage under Egyptian conditions during 2012/2013 growing season. Lines LB-Iran and F6-1-KF showed the resistance to all isolates and lowest ratings of disease severity of 18.75 and 20.31% respectively, while the remaining lines showed intermediate ratings resistance to isolates and disease severity ranging from 39.06 to 46.88%. The commercial varieties showed that about of resistant to all isolates ranging from 6.25 to 43.75% and highest ratings of disease severity ranging from 64.06 to 85.94%. Giza 2000 is the best commercial variety for resistant to isolates and lowest of the diseases severity was 43.75 and 64.06% respectively. Proteins of different genotypes were separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) from healthy and diseased plants at adult stage. Two bands with MW 70 and 24 KDa were found only in healthy plants of resistant genotypes, and absent from susceptible genotypes. These protein markers could be used to qualitatively differentiate between resistant and susceptible genotypes. Linear regression analysis constructed one factor model to predict powdery mildew severity. This model indicated that a protein with MW 71 KDa accounted for 63.19% of the total variation in severity ratings. This result indicates that SDS-PAGE of plant proteins may provide a supplementary assay to field tests to distinguish quantitatively between Powdery mildew resistant or susceptible genotypes