The purpose of this study was to identify the relationship of symptom distress and natural killer cell cytotoxicity in breast cancer patients who had been radiation therapy and/or chemotherapy after surgery. Symptom distress measured by modified Lee's(1994) physical symptom questionnaire. For measuring the natural killer cell cytotoxic activity, 8ml to 10ml blood was collected from the subjects. Mononuclear cell was isolated by centrifuge of the blood and cultured by putting Cr⁵¹, and reacted with target cell, K562 cell. Amount of Cr⁵¹ was measured, and %lysis was calculated. The results were as follows. 1) Symptom distress score was 42.18, which is moderate symptom distress. 2) Natural killer cell cytotoxic activities were 42.18%lysis(effector : target cell ratio=100 : 1) and 28.05%lysis(effector : target cell ratio=50 : 1). 3) Correlation coefficients of symptom distress and natural killer cell cytotoxic activity were .134~-.461. Though significant correlation was not found between total score of symptom distress and natural killer cell cytotoxic activity, 3('pain' 'feel hot on radiation site' and 'difficulty in breathing') of 19 symptom distress items and natural killer cell cytotoxic activity showed significant negative correlation(p<.05). These findings suggest that 1) breast cancer patients who had been radiation therapy and/or chemotherapy after surgery have moderate symptom distress and decreased natural killer cell cytotoxic activity. 2) The symptom distress was not related to natural killer cell cytotoxic activity.