Background. Even though medications play a major role in the cure, palliation, and inhibition of disease, they also expose patients to drug-related problems. Drug-related problems are frequent and may result in reduced quality of life, morbidity, and mortality.Objectives.e study was aimed to identify, characterize, and resolve drug-related problems in the Pediatric Hematology/ Oncology ward of Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia. Methods. A prospective observational study was conducted from 25 June to 25 October 2018 to assess DRPs on patients admitted at the pediatric hematology/oncology ward of Tikur Anbessa Specialized Hospital, which is the highest level governmental tertiary care hospital in Ethiopia. Data were obtained from patients' medical charts, physicians, patients/caregivers, pharmacists, and nurses. All the collected data were entered and analyzed using the Statistical Package for the Social Sciences version 25e. Descriptive statistics were used to represent the data. Results. Among the total 156 participants, DRPs were identified in 68.6% of the study subjects. Dosing problems which include dosage too low and high were the top ranking (39.3%) of all DRPs followed by needs additional therapy (27.2%) and nonadherence (14.0%). Systemic anti-infectives were the most common class of drugs involved in DRPs. Trimethoprim-sulfamethoxazole, methotrexate, vincristine, ondansetron, and metoclopramide were frequently involved in DRPs. e addition of drugs and change in drug dose were the two most proposed intervention types. Among the proposed interventions, 223 (92.15%) were fully accepted, 9 (3.72%) partially accepted, and 10 (4.13%) not accepted. Conclusion. DRPs are common among Pediatric Hematology/ Oncology ward patients. e hospital should develop a pediatric dosing chart for the commonly prescribed medications to prevent drug-related morbidity and mortality. e integration of clinical pharmacists can mitigate risks associated with DRPs.