Studies investigating the effects of relaxation practices on nurses and patient outcomes are limited. This study aimed to evaluate the impact of Mindfulness-Based Stress Reduction (MBSR) on pediatric oncology nurses' stress levels, as well as the psychosocial symptoms and care satisfaction of pediatric oncology patients. A non-randomized prospective study with a pretest-posttest design was conducted, involving 112 children and 8 pediatric oncology nurses between November 2021 and August 2022. The study was conducted in 3 stages. First, the children's nursing care satisfaction and psychosocial symptoms were evaluated during the first 3 months before the MBSR intervention. Second, the nurses participated in the MBSR program for 2 months. Third, the children's nursing care satisfaction and psychosocial symptoms were assessed again 3 months after the MBSR intervention. The results showed that children who received nursing care post-MBSR had lower scores in the Psychosocial, Hopelessness, and Communication Difficulty subscales compared to those who received care pre-MBSR. Additionally, these children had higher scores in Evaluation of Quality of Care from the Children's Point of View, Psychosocial, Physical, and Information subscales. There was a significant reduction in the stress levels of nurses between the pre-MBSR and post-MBSR assessments. MBSR is an effective method for reducing pediatric oncology nurses' perceived stress levels and should be utilized to support both pediatric oncology nurses and patients in enhancing their psychosocial functioning.