The present study was carried on forty (40) diagnosed ALL (Acute lymphoblastic leukemia), CML (Chronic myeloid leukemia), AML(Acute myeloid leukemia)patients who attended Oncology Centre, Mansoura University. Their ages ranged from 3 to 77 years. They were 27 males and 13 female. Patients were followed up throughout the period of the study. All patients were subjected to the following: Detailed history, clinical examination and Laboratory investigations. Results: CD40 expression was not associated with any of the studied demographic, clinical or laboratory variables. No statistically significant associations were elicited between CD40 expression and any of the studied prognostic factors of patients.  However, a significant positive association was detected between patients who responded to chemotherapy and positive CD40L. Conclusion: CD40L is an independent prognostic factor for relapse free survival, and also an independent prognostic factor for the prediction of good response to chemotherapy, since CD40L positive patients are more liable to achieve complete remission, while CD40 negative ones are more susceptible to death chemotherapeutic resistance.