Background: The study investigates the nutritional status in children with acute lymphoblastic leukemia (ALL) during chemotherapy treatment because nourishment is substantial, as much as chemotherapy in children with malignant diseases. Material and Method: We enrolled 17 children with ALL (between 1 to 16 year-old, mean age 6.03 ± 4.04 y) from 5 different centers in Istanbul between September 2013 and May 2014. Anthropometric data, prealbumin, B12, and folate levels were assessed, at diagnosis, after the induction phase of chemotherapy, and before maintenance phases of chemotherapy in a longitudinal and prospective study. Results: Patients remarkably lost weight at the end of the induction phase (P=0.064) and regained this loss before maintenance chemotherapy (P=0.001). At the end of induction chemotherapy serum prealbumin level (P=0.002), weight for height ratios (P=0.016), weight for age ratios (P=0.019) significantly decreased. From the end of the induction phase to the beginning of maintenance chemotherapy, weight (P=0.001) and weight for age (P=0.017) significantly, and weight for height were remarkably elevated (P=0.076). At the end of the induction phase, serum prealbumin levels were significantly lower (P=0.048) and below laboratory reference values (P=0.009) in children younger than 60 months compared with those older. Serum folate levels increased from the end of the induction phase to the beginning of the maintenance phase (P=0.025). Serum vitamin B12 levels did not alter significantly. Conclusion: There is malnutrition risk at the end of the induction phase of the ALL-BFM chemotherapy regimen; therefore, clinicians should follow up on nutrition closely, especially in under 5-year-old patients. However, before the beginning of the maintenance phase, children start to gain weight, and obesity risk occurs. Thus, further studies are needed to evaluate nutritional status during childhood ALL chemotherapy.