Breast cancer (Carcinoma mammae) is a malignant tumor that grows in the breast tissue. This cancer begins to grow in the mammary glands, fat tissue, and connective tissue in the breast. Management of breast cancer depends on the type and stage experienced by the patient. One of the therapies given to breast cancer is chemotherapy. This research was conducted with the aim of knowing the side effects of chemotherapy in breast cancer patients at Jayapura Hospital. This type of research was conducted using a descriptive method, with a population of patients at the Jayapura Regional General Hospital. 81 respondents were taken as a sample. This research was conducted from April to May 2023. The results showed that the characteristics of respondents at the Jayapura Regional General Hospital were based on age, the highest being in the age group 36–47 years (56%). High school education (32%) and other jobs (housewife, labor) (47%). Marital status The highest respondent was married with 66 patients (82%). Symptoms of Side Effects of Chemotherapy Began to Appear in breast cancer patients at Jayapura Hospital 3 days after chemotherapy, namely 47 patients (58%). Side Effects of Chemotherapy Breast cancer patients who received chemotherapy at Jayapura Hospital with symptoms namely, Alopecia in 81 patients (100%), Nausea & Vomiting in 79 patients (98%), Myalgia in 76 patients (94%), Leukopenia in 64 patients (79%), Anemia in 62 patients (77%), Neuropathy in 62 patients (77%), Stomatitis in 27 patients (33%), Diarrhea in 25 patients (43%), Thrombocytopenia in 21 patients (26%) and allergies as many as 9 patients (11%), the type of regimen most often used in breast cancer patients in TA was 30 patients (37%).