Acute lymphoblastic leukemia with eosinophilia (ALLEo) is a rare but a distinctive clinical entity. Clinical features of idiopathic hyper-eosinophilic syndrome (HES) can be seen in patients with ALLEo. We report a 10-year-old girl, in whom HES was initially suspected but further investigation confirmed the diagnosis of acute B-cell lymphoblastic leukemia with myeloid antigen expression. Clinical response to chemotherapy was excellent with achievement of complete remission for 4 years. Serum interleukin-3 and -5 were elevated at presentation and normalized with disappearance of eosinophilia after induction therapy, supporting the reactive nature of eosinophilia in ALLEo. Hematologic malignancy should be considered in patients with hyper-eosinophilia, before attributing it to HES.