Several molecular epidemiological studies were conducted in recent years to evaluate the association between NQO1 Pro187Ser polymorphism and breast cancer risk in diverse populations. However, the results remain conflicting rather than conclusive. This meta-analysis on 3177 cases with breast cancer and 4038 controls from seven published case-control studies showed that the 187Ser allele was not associated with a significantly increased risk of breast cancer (Ser versus Pro: P = 0.33, OR = 1.08, 95% CI = 0.92-1.28; Ser/Ser versus Pro/Pro: P = 0.58, OR = 1.16, 95% CI = 0.68-2.00; Ser/Ser versus Pro/Ser + Pro/Pro: P = 0.62, OR = 1.14, 95% CI = 0.68-1.90; Ser/Ser + Pro/Ser versus Pro/Pro: P = 0.30, OR = 1.07, 95% CI = 0.94-1.22). In the stratified analysis by ethnicity, we found that the Pro187Ser polymorphism was associated with increased breast cancer risk in Caucasians in the additive genetic model and dominant genetic model (P = 0.03, OR = 1.13, 95% CI = 1.01-1.26; P = 0.03, OR = 1.15, 95% CI = 1.01-1.30, respectively), whereas no significant in Asians (P = 0.44, OR = 0.94, 95% CI = 0.80-1.10) and postmenopausal women (P = 0.99, OR = 1.00, 95% CI = 0.84-1.19). The results suggest that NQO1 Pro187Ser polymorphism may contribute to breast cancer development in Caucasians.