Atopic dermatitis is an itchy, chronic or chronically relapsing, inflammatory skin condition. Many cytokines participate in the inflammatory response of the disease. The aim of this work was to study the role of Th9 cells,PU.1 and IL-9 in the pathogenesis of atopic dermatitis. This study was conducted on three groups, atopic dermatitis patients group composed of thirty patients diagnosed as having atopic dermatitis according to the criteria of Hanifin and Rajka (Hanifin & Rajka,1980), psoriasis control group consisting of thirty control psoriasis patients and a healthy control group comprising thirty healthy age and sex-matched control subjects. All atopic dermatitis patients were examined for determination of their SCORAD score. IL-9, PU.1 expression levels were determined by RQ-PCR and serum Ig E level by ELISA in all groups. The current study showed that IL-9, PU1expression levels and serum IgE levels showed statistically significant higher levels in AD patients compared with the psoriatic and healthy control subjects. In the present study there was also a statistically significant correlation between SCORAD index and each of IL9, PU.1 expression levels and serum IgE level suggesting that they can be used as markers of disease severity. There were no statistically significant differences between patients with positive personal history of other atopic disorders and patients with negative personal history of other atopic disorders regarding IL9, PU.1 expression levels which suggests that the increased levels could be due to atopic dermatitis and not secondary to other allergic diseases.