Background: Alopecia areata (AA) is a chronic inflammatory disease that involves the hair follicle. Transforming growth factor β- is a multipurpose cytokine which plays a role in many cellular functions such as proliferation, differentiation, migration, apoptosis, cell adhesion and regulation of epithelial to mesenchymal transition. Aim; the aim of this work was to evaluate the serum levels of TGF-β1 in patients with AA by ELISA and correlate its level with severity. Methods: This study included sixty clinically diagnosed patients with AA, their ages ranged from five to fivty years and twinty five apparently healthy subjects were served as control. All studied individuals were subjected to history taking and clinical assessment of lesions according to clinical severity into mild, moderate and severe. We investigated serum level of TGF-β1 using Enzyme-linked immunosorbent assay. Results: there wasa highly statistically significant difference was found between the mean serum TGF-β1 level of cases vs. controls. TGF- β1 level of severe AA patients was higher than moderate AA patients and moderate cases were higher than mild cases. The level of TGF-β1 was higher in AA patients that had disease duration > one month than AA patients with disease duration≤ one month. There were statistically significant differences of serum TGF-β1 as regard age, higher in patients> 10 years old and nail pitting, higher in patients with nail pitting. Conclusion: High levels of TGF-β1 are present in patients with AA and positively correlate with severity, which may indicate a causal role of TGF-β1in pathogenesis of AA.