Abstract: Objective To explore the association between urinary molybdenum and the risk of breast cancer. Methods Questionnaire survey and urine sample collection were applied on 240 female breast cancer patients and 246 healthy and age-matched controls in two Affiliated Hospitals of Sun Yat-sen University from Oct. 2009 to July 2010. Rank test and multivariate analysis were used to estimate the association between urinary molybdenum and risk of breast cancer. Results Creatinine-adjusted urine levels of molybdenum (median μg/g) were 85.20 μg/g in female breast cancer patients and 72.68 μg/g in the controls, with statistically significant difference. There was a tendency that the intermediate tertile was associated with a lower risk of breast cancer while the highest tertile increased the risk of breast cancer, compared with the lowest tertile, with no statistical significance. Postmenopausal women in the highest tertile of urine molybdenum showed a significant increased risk of breast cancer, compared with those in the lowest tertile (OR=2.35, 95%CI=1.13-4.92). Conclusion A moderate level of Molybdenum may have inhibitory effect of breast cancer; while a high level of Molybdenum may increase the risk of breast cancer, especially for postmenopausal women.