This study was conducted to investigate the relationship between alcohol consumption, physical activity and breast cancer risk in Korean women. Newly histologically identified cases (N = 108) were selected at Hanyang and Soonchunhyang University Hospitals in Seoul, from January 1998 to August 1999. Hospital-based controls (n = 121) were the patients who visited at the same hospital in the department of plastic surgery, general surgery and opthalmology. Subjects were asked informations on demographic, reproductive, and history of breast feeding as well as physical activity, exercise habit, alcohol consumption by individual interview. Odds ratio (OR) and 95% Confidence Intervals (CI) were calculated by using unconditional logistic regression after adjusted for confounding factors. Among postmenopausal women, the risk of breast cancer increased with increasing alcohol drinking: relative risk for the highest group ( $geq$ 150 g per week) compared with the lowest group (never drinking) was 2.05 (CI=1.74-3.79). Association of exercise and high physical activity for breast cancer appeared to be limited to women with high physical index among postmenopausal women. We observed decreasing risk of breast cancer with increasing physical activity index among postmenopausal women (OR=0.49,95% CI=0.56-0.92). Results of this study support a protective effects of physical activity during adulthood for breast cancer. (Korean J Nutrition 36(1): 40-48, 2003)