Thalassemia patients who do not receive adequate transfusion are at risk of splenomegaly and growth impairment. This study was conducted to evaluate the relation between pre-transfusion hemoglobin (Hb) level with spleen size and body height, also the relation between spleen size and the risk of neutropenia and thrombocytopenia. This was a retrospective study involving 171 non-splenectomized children with thalassemia major. The study was conducted in Dr Cipto Mangunkusumo National Hospital, Jakarta and used data from the past year (2017-2018). Mean pre-transfusion Hb level, neutrophil and thrombocyte count was measured for one year. Mean pre-transfusion Hb level was divided into high (Hb ≥9 g/dL) and low (Hb <9 g/dL). The results showed significant difference of spleen size between subject with high and low pre-transfusion Hb level, but not for the prevalence of stunted. Moderate to massive splenomegaly (spleen size greater than Schuffner 2) increases risk of thrombocytopenia (OR 9.40, p<0.0001), but not for neutropenia (p=0.477). Therefore, it is concluded that maintaining high pre-transfusion Hb level ≥9 g/dL brings many benefits because it prevents the occurrence of complications in children with thalassemia major.