Abstract Objective Chemotherapy and radiotherapy, used to treat childhood hematological malignancies (acute lymphocytic leukemia [ALL] and acute myelocytic leukemia [AML]) can negatively affect oral tissues and organs. This study aimed to evaluate the oral health‐related quality of life in children with ALL/AML. Materials and Methods A total of 99 children, including 49 undergoing ALL/AML (41 with ALL and eight with AML) and 50 healthy volunteers, were included in this cross‐sectional study. The mean age of the entire study group was 78.63 ± 34.41 months. The mean age of the ALL/AML and control groups was 87.12 ± 35.04 and 70.95 ± 34.85 months, respectively. The Simplified Oral Hygiene Index (SOHI), the Decayed, Missing, and Filled Teeth (DMFT/dmft) index, and the Turkish version of the Early Childhood Oral Health Impact Scale (ECOHIS‐T) were administered to all children. The data were analyzed using SPSS software (version 22.0). The Pearson chi‐square and Fisher's exact tests were used to compare demographic data. Results The age and gender distributions of the two groups were similar. According to ECOHIS‐T, the children in the ALL/AML group had significantly more loss of function (eating, drinking, sleeping, etc.) than those in the control group. Conclusions Oral health and self‐care were negatively affected by childhood ALL/AML and its treatment.