Breast cancer and its treatment especially chemotherapy-related symptoms may greatly affect the nutritional status of the patient so good nutrition are important especially during treatment , it can lead to better outcomes for breast cancer treatment. Aim of the study: to determine the effect of nutritional teaching program on clinical outcomes for breast cancer patients undergoing chemotherapy. Research design: Quasi-Experimental design was utilized in this study, Subjects and setting: A convenience sample of 60 patients who had primary breast cancer at Clinical Oncology and Nuclear Medicine Department at Tanta University Hospital in the specialized chemotherapeutic wards and in outpatient's clinic. ; The sample was divided randomly and equally into two groups; control group was received routine hospital nutrition and study group who received nutritional teaching program and routine hospital. Tools of data collection: two tools were used, tool I: structured interview schedule. Tool II: "Nutritional status assessment tool consisted of four parts: Part (1) physical examination, physiological parameter, signs and symptoms of nutritional deficiency .Part (2): Dietary intake. Part (3) Anthropometric measurements observational checklist .Part (4): laboratory data. Results indicated that there were highly statistically significant differences between study and control groups throughout the study period regarding mean knowledge P= (0.012, 0.008 and 0.019) respectively, regarding pale skin, fatigue ,weakness, alopecia, constipation and vertigo in the third month after chemotherapy sessions since p=( 0.002, 0.010, 0.044, 0.020, 0.020 and 0.010) respectively. Conclusion: It can be concluded that early nutritional teaching program before beginning chemotherapy session and during chemotherapy periods is very effective on reducing chemotherapy side effects and improving health status. Recommendation nutritional support, advice and guidelines by dietician and nurse of the nutritional regimen should be undertaken for patients undergoing chemotherapy