Reactive oxygen species (ROS), normally generated through biologic processes, may damage DNA, lipids, and proteins. ROS are balanced through enzymatic mechanisms and exogenous antioxidants; imbalance results in oxidative stress. Limited data suggest an association between oxidative stress and breast cancer. We evaluated pre-diagnostic plasma fluorescent oxidation products (FlOP), a global biomarker of oxidative stress, and breast cancer risk in a nested case–control study in the Nurses’ Health Study. Participants provided two blood samples (1989–1990 and 2000–2002) (N = 18,743). 377 women developed breast cancer between the second collection and June 1, 2006. Cases were matched to 377 controls. Relative fluorescent intensity at three different excitation/emission wavelengths (FlOP_360, FlOP_320, FlOP_400) were quantified in both samples, providing distant (≥10 years before diagnosis) and proximate (≤6 years before diagnosis) measures of oxidative stress. We observed no association between FlOP and breast cancer risk in proximate or distant samples (e.g., proximate extreme quartiles: FlOP_360, RR 0.8, 95 % CI 0.5–1.3, p _trend = 0.49; FlOP_320, RR 1.1, 95 % CI 0.7–1.7, p _trend = 0.53; FlOP_400, RR 1.3, 95 % CI 0.8–2.0, p _trend = 0.80). In general no association was observed when cross-classifying or averaging proximate and distant exposure (e.g., extreme quartile of averages: FlOP_360, OR 0.9, 95 % CI 0.6–1.4, p _trend = 0.82; FlOP_400, OR 0.9, 95 % CI 0.6–1.4, p _trend = 0.55), with the exception of a significant trend for average FlOP_320 (extreme quartiles, OR 1.6, 95 % CI 1.0–2.4, p _trend = 0.02). We did not observe important associations between FlOP and breast cancer risk in this large prospective study, though our data suggest women with consistently high FlOP_320 may be at increased risk.