Nine clay soil samples were obtained from different flax-growing areas. The relationships of powdery mildew intensity variables (PMIV) to 22 physical and chemical factors of these soils were studied by simple correlation and stepwise regression analysis. It was found that nitrogen (ppm), potassium (ppm), iron (ppm), Cl^- (meq/100 g soil), Ca⁺⁺ (meq/100 g soil), Mg⁺⁺ (meq/100 g soil), Na⁺ (meq/100 g soil), electric conductivity (ds/m), coarse sand (%), and fine sand (%) were the most important edaphic factors contributing to PMIV. Of these factors, potassium, Mg⁺⁺, and fine sand were negatively correlated with PMIV, while the others were positively correlated. Coefficient of determinations (R²) of the 4 regression models that described the relationship between PMIV and edaphic factors ranged from 74.66-100%. The results of the present study demonstrated that under Egyptian soil conditions, certain physical and chemical edaphic factors affect development of powdery on flax, and that control of the disease may be possible by modifying the nutritional status of the plant.