Eight flax cultivar were evaluated for powdery mildew resistance under field conditions , C.I. 2008, Cortland, Linore and the local cultivars Giza 8 , Giza 7 were highly susceptible. Disease severities on these cultivars were 100.00, 99.48 and 95.26 , 93.46 and 87.26%respectively. On the other hand, cultivars Williston brown, Wilden and Dokota were highly resistant,with disease severities on these cultivars were 27.58, 25.11 and 19.67%, respectively. SDS-PAGE, RAPD analysis by using four primers and double diffusion test (DDT) were used to differentiate between resistance and susceptible genotypes. RAPD analysis by using primer no. 6 and DDT were able, at least partially, to differentiate between resistant and susceptible genotypes, while SDS-PAGE was unable to differentiate between cultivars of the two groups.