Background. Breast cancer is the main cause of death for women. One of the therapies for breast cancer is chemotherapy. Chemotherapy has physical and psychological side effects. Patients need to adapt in order to be able to follow the process of chemotherapy treatment, and supportive group therapy is one of the ways to improve adaptation ability of patients. The aim of this study was to analyze supportive group therapies in improving the psychological adaptation of breast cancer patients undergoing chemotherapy. Method. This study uses pre-experimental one group pretest-posttest design. The sample consists of 35 respondents that were divided into 3 groups during the treatment. Pre-test and post-test were conducted to each group by using Likert scale. This study uses sampling technique of purposive sampling with inclusion criteria. Results. Before supportive group therapy is conducted, the average score of the respondents are 35,85 meanwhile after the supportive group therapy is conducted the average score increases to 43,82. The statistical analysis by using paired t-test shows that p-value.000 < 0,05 and this demonstrates that the supportive group therapy can improve psychology adaptation of breast cancer patient who undergone chemotherapy. Conclusions. Supportive group therapy can be an alternative to support the breast cancer patients to adapt and undergone chemotherapy. © 2018, Indian Journal of Public Health Research and Development. All rights reserved.