Background: Breast cancer brings negative impacts to women, particularly those who have undergone chemotherapy, not only physically but also mentally. The negative impacts on patients’ mental include a feeling of being failed playing their role as a woman, not having abilities to do anything, low self-esteem, and confidence loss. Thus, family support is necessary in anticipating negative self-esteem in breast cancer patients. Family support helps the patients maintain and increase their self-esteem. Objective: The objective of this study is to analyze the relationship between family support and self-esteem in patients with breast cancer undergoing chemotherapy at Haj Adam Malik Central Hospital. Methods: The study employed analytical correlational design with cross sectional approach. The research samples included all breast cancer patients who were undergoing chemotherapy at Haj Adam Malik Central Hospital in Medan City. The sampling selection of this study used total sampling technique; hence the total sample number was 34. Spearman test was performed in data analysis. Result: The study suggested that 64.7% of the respondents received good family support and 66.7% of the respondents had high level of self-esteem. Besides, it was also obtained that there was a moderate correlation between family support and self-esteem of patients with breast cancer (p=0.01< α 0,05 with r = 0.432). The results imply that the better family support is the higher the level of self-esteem of patients with breast cancer undergoing chemotherapy will be. Therefore, it is recommended that each of family members gives support to patient in the form of care, information, and instrumental support, so that the patient will have better self-esteem and quality of life.