Background: Immune thrombocytopenia is an auto immune disorder characterized by low platelet count due to either peripheral platelet destruction or inappropriate production of platelets by bone marrow. although auto antibodies have been showed as the principle factor in the pathogenesis of ITP, also cellular immune modulation have been identified to have a very important role in the pathophysiology of ITP. the aim of this study was to investigate runt related transcription factor 1 (Runx1) and it`s association to ITP. Aim of the Work: To determine the expression levels of runt related transcription factor in the peripheral blood of children with ITP and to determine the clinical usefulness of this transcription factor in understanding the pathophysiology of ITP and its relation to disease activity and chronicity. Patients and Methods: This study was conducted on 49 patients having ITP in beni-suef university hospital and 20 healthy subjects as controls. RUNX1 was analyzed using ELISA technique. Results: The results revealed that RUNX-1 levels were significantly higher in ITP patients compared to controls (1.78 ±0.73 vs. 3.87 ±2.39, p=0.001) in healthy controls and ITP patients respectively. Conclusion: RUNX1 is involved in the pathogenesis of ITP, it also related to disease activity