Purpose: The purpose of this study was to identify the factors affecting symptom experiences of breast cancer patients. Methods: A cross-sectional descriptive study was conducted with based on the Unpleasant symptom Theory. Sixty breast cancer patients were recruited. We measured their symptom experiences, physiologic factors (immune system function and specific perceived symptoms), psychological factors (depression and anxiety), and situational factors (family support). After obtaining permission from the IRB, data were collected from self-report questionnaires and electronic medical records from a single cancer center. Descriptive statistics, t-test, one-way ANOVA, correlations and multiple regressions were used to analyze the data. Results: The most frequent and severe symptoms were fatigue ($4.47{pm}2.99$), numbness or tingling ($3.67{pm}3.08$) and sadness ($3.45{pm}3.64$). Symptom experiences were significantly positively correlated with psychological factors (r=.603, p<.01) and physical symptoms (r=.384, p<.01). Symptom experiences and situational factors (r=.302, p<.05) were had a significantly negative correlation. The factor that had the most impact on symptom experiences were psychological factors, followed by perceived physical symptoms. The regression model explained 44.8% of the variances. Conclusion: Based on the results of this study, the physiological, psychological and situational factors should be considered for caring breast cancer patients.