Wheat powdery mildew caused by Blumeria graminis f. sp. tritici has recently assumed significance affecting wheat production under Egyptian conditions. Relationship between yield reduction and grain quality and the disease were studied during 2012/13 and 2013/14 growing seasons at Gemmeiza Agricultural Research Station on 9 wheat varieties i.e. Sakha 93, Giza 168, Gemmeiza 7, Gemmeiza  9, Gemmeiza 10, Gemmeiza  11, Misr 1, Misr 2 and Sids 12. Disease severity was 4.33 % to 41.66 % in 2012/13, 8.33 % to 51.66 % in 2013/14. Area under disease progress curve (AUDPC) was found to be correlated with powdery mildew severity during the two growing seasons. The highest loss in 1000 kernel weight was recorded on Sakha 93. On the other hand, Sids 12 showed the lowest loss during 2012/13 (1.13%), whereas Misr 2 showed the lowest loss in 2013/14 season (1.2%). Regarding the effect of the disease on grain quality, the highest increase in protein content was observed on Sakha 93( 14.14% -15.85%) ,whereas  Giza 168 showed the least increase in protein content .The most affected wheat cultivar in carbohydrate content  was found in Gemmeiza 7 (6.64%). Increase % in wet gluten content varied from season to season, Gemmeiza 11 exhibit the highest value , whereas Giza 168and Sakha 93 revealed the least change.