Cumulative evidence suggests a possible interaction of cooking methods with diet in the pathogenesis of breast cancer. Studies, however, are few and inconsistent. We evaluated the association of animal food intake and degree of browning by deep-frying with breast cancer risk in a population-based case-control study conducted during 1996-1998 among Chinese women in Shanghai, a population with a traditionally low risk of breast cancer. Included in the study were 1459 cases and 1556 age-frequency-matched controls with response rates of 91.1 and 90.3%, respectively. A validated food frequency questionnaire was used to obtain information on usual intake of animal foods and cooking oils and usual cooking methods. Increasing intake of red meat and freshwater fish was related to a moderately elevated risk of breast cancer risk. Stratified analyses showed that the positive association with red meat intake was primarily restricted to those who used deep-frying cooking method, particularly among those who deep-fried foods to well-done (odds ratio, 1.92; 95% confidence interval, 1.30-2.83 for the highest versus the lowest quintile; P for trend, 0.002). On the other hand, high intake of nonhydrogenated soybean cooking oil was related to a reduced risk of breast cancer among women who never deep-fried animal foods (odds ratio, 0.48; 95% confidence interval, 0.28-0.82 for the highest versus the lowest quintile; P for trend, 0.02). The positive association of breast cancer risk with red meat intake, especially well-done red meat, was more pronounced among women with a high body mass index than those without this risk factor, and the test for multiplicative interaction was statistically significant. This study suggests that high intake of deep-fried, well-done red meat may be associated with an increased risk of breast cancer, and the positive association may be modified by body weight. This study also suggests that nonhydrogenated soybean oil, if not used in high-temperature cooking, may be associated with a reduced risk of breast cancer.