Background: Cancer patients undergoing radiotherapy experience a variety of physical and psychosocial side effects. Aim of the study: To evaluate the effect of educational nursing guidelines on minimizing side effects for cancer patients undergoing radiotherapy. Patients and Methods: Research design: A quiz–experimental (pretest / post-test) research design was utilized. Setting: The study was conducted in Clinical Oncology Department at Assiut University Hospital. Sample: A convenience sample of sixty male and female adult cancer patients undergoing radiotherapy. Tool: Interview questionnaire sheet which included Patient assessment and memorial symptom assessment scale. Results: Statistical significant differences were found between pre and post applying of the educational nursing guidelines as regard physical symptom subscale score, psychological symptom subscale score, global distress index score, and total memorial symptom assessment scale score. (p<0.01). Conclusion: The educational nursing guidelines had a statistical significant positive effect on minimizing the side effects for cancer patients undergoing radiotherapy. Recommendation: Each cancer patient undergoing radiotherapy should be given an educational booklet including guidelines to minimize side effects of radiotherapy. Key Words: Educational guidelines, Side effects, Radiotherapy.