Background: Bone marrow transplantation is a medical procedure that is performed to replace bone marrow or stem cells that has been destroyed by disease especially certain types of malignant (cancerous) and nonmalignant (noncancerous) diseases. Aim of study: Was to evaluate the effect of designed educational guidelines on nurses’ performance regarding management of children undergoing bone marrow transplantation. Design: A quasi-experimental research design was utilized to conduct this study. Settings: This study was carried out in Bone Marrow Transplantation Unit of Mansoura university children hospital affiliated to Mansoura University Hospital, Tanta University Educational Hospital affiliated to Tanta University Hospital and Nasser Institute affiliated to Specialized Medical Centers. Subject: A convenient sample included (57) nurses who are providing direct care for children undergoing bone marrow transplantation at previously mentioned settings. Tools of data collection: Data were collected by using tools which are: Tool (I): A structured interviewing questionnaire sheet. Tool (II): Observation checklist for nurses' practice to evaluate nursing practice before and after implementation of designed educational guidelines regarding bone marrow transplantation. Results: The majority of the studied nurses had satisfactory level of total knowledge regarding bone marrow transplantation post-designed educational guidelines compared to pre-designed educational guidelines implementation. Also, the majority of the studied nurses had competent level of total practice in post designed educational guidelines compared to pre designed educational guidelines implementation. Conclusion: The designed educational guidelines were effective in improving nurses` performance regarding management of children undergoing bone marrow transplantation. Also, there was a positive correlation between nurses’ total level of knowledge and total practice at pre and post designed educational guidelines implementation. Recommendations: Conducting continuous training programs about bone marrow transplantation for nurses to enhance their knowledge and practice.