The purpose of this study was to identify how mood disturbance and social support were related to the symptoms experienced by Korean women with breast cancer. A cross-sectional, correlational design was used for the study. A convenience sample of 134 Korean women receiving chemotherapy for breast cancer was recruited. The participants completed questionnaires on symptom experience using the Symptom Experience Scale, mood disturbance using the Linear Analogue Self-Assessment Scale, and social support using the Social Support Scale. Mood disturbance and social support had a significant interaction effect on symptom experience. A higher level of mood disturbance led to a higher level of symptoms when the level of social support was average or low, which implies that clinical interventions for attenuating the impact of mood disturbance on symptom experience might be effective only for women perceiving average or low levels of social support.