Background: Childhood leukemia represents one of the most prevalent types of cancer. Chemotherapy is the cornerstone of leukemia management. Essentially, it can cause a deficiency in food and liquid consumption, electrolyte imbalance, weight loss, and consequently nutritional disorders. Healthy nutrition is pivotal for children's nutritional needs for optimal growth and to support them during chemotherapy. Objective: To evaluate the effect of dietary educational programs on knowledge and the nutritional status of children with leukemia undergoing chemotherapy in Sana'a Yemen. Settings: The study was conducted in the Childhood Leukemia Treatment Unit at Al-Kuwait Hospital in Sana'a Yemen. Subjects: All available children with leukemia undergoing chemotherapy for six months at the previously mentioned setting and fulfilled the inclusion criteria. Tools: Three tools were used namely; Children's Knowledge about Nutritional Status during Chemotherapy Structured Interview Schedule, Twenty-Four-Hour Dietary Recall Assessment Sheet, and Anthropometric Measurements of Children with Leukemia Undergoing Chemotherapy. Results: The study revealed that the nutritional knowledge of children with leukemia undergoing chemotherapy was significantly increased after the dietary educational program implementation than before and their nutritional status exhibited of significantly higher improvement after the dietary educational program implementation than before (P < 0.001 for each).Conclusion: All children with leukemia undergoing chemotherapy had poor total scores of nutritional knowledge before implementing the program. Fortunately, all children with leukemia undergoing chemotherapy had good total scores immediately after and three months later after the dietary educational program implementation. Recommendations: The recent guidelines for nutritional assessment and management of children with leukemia undergoing chemotherapy should be applied by pediatric oncology nurses in the Childhood Leukemia Treatment Unit.