Breast cancer is the most common type of cancer in women worldwide. Treatment of breast cancer often consists of a combination of surgical intervention, radiation therapy and medication (chemotherapy ,hormonal therapy and/or targeted biological therapy). Chemotherapy is an important therapeutic option for women with breast cancer but is often associated with unpleasant side effects. Aim of the study: To evaluate the effect of designated health promotion program on the incidence of side effects of chemotherapy among breast cancer patients. Research design: A quasi experimental research design. Setting: Oncology outpatient clinic in Fayoum University Hospital. Methods: A purposive sample of 60 adult patients from previously mentioned setting, allocated randomly into two equal groups (30 patients in each). Tools: Four tools were utilized, included: Structured Interview questionnaire, patients knowledge assessment questionnaire, patient’s self-care practice questionnaire, Chemotherapy Side Effects Questionnaire. Results: There was a statistical significant difference between both groups as regarding knowledge (p-value= 0.002*), self-care practices (p-value= 0.004*) and incidence of side effects of chemotherapy post implementation of designated health promotion program with higher percentage of side effects of chemotherapy among control group. Conclusion: Application of the designated health promotion program had a positive effect on the outcomes of breast cancer patients undergoing chemotherapy. Recommendations: Apply the designated health promotion program to all cancer patients undergoing chemotherapy.