Objective:To investigate the effects of exposure to ambient particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) on systemic oxidative stress biomarkers in chronic obstructive pulmonary disease (COPD) patients.Methods: A panel of forty-five diagnosed and stable COPD patients, whose residences were within 5 kilometers from Peking University Health Science Center (PKUHSC), were recruited and followed up twice between November 2014 and May 2015.The lung function index percentage of forced expiratory volume in 1 second (FEV1) to predicted value (FEV1%pred), was measured to reflect the severity of COPD patients.The systemic oxidative stress biomarkers malondialdehyde (MDA) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) in their urine samples were measured using high performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), respectively.Concentrations of ambient air pollutants and levels of meteorological factors were measured continuously through the air pollution-monitoring station located in PKUHSC.PM2.5 samples, which were used for measuring the concentrations of PAHs, were collected by PM2.5 high volume air sampler.We constructed linear mixed-effects models, including single-pollutant model, 2-pollutant models and stratification analysis, to estimate the effects of air pollutants on urinary MDA and 8-OHdG after adjusting for confounding factors.Results: In our COPD-patient panel, the associations between ultrafine particles (UFP) and PAHs and urinary MDA were statistically significant at lag2 (P<0.05).For an interquartile range (IQR) increase in UFP and PAHs, respective increases of 28% (95%CI: 4%-57%) and 36% (95%CI: 4%-77%) in urinary MDA were observed, and the effects became stronger after adjusting for the concentration of black carbon (BC).The COPD patients were divided into 2 groups stratified by FEV1%pred.Most air pollutants had stronger effects of systemic oxidative stress in the COPD patients of FEV1%pred≥50%.In this group, we observed that an IQR increase in UFP was associated with a 98% (95%CI: 38%-186%) increase in urinary MDA, and an IQR increase in BC, UFP and PAHs were associated with respective increases of 87% (95%CI: 32%-166%), 69% (95%CI: 24%-130%) and 156% (95%CI: 66%-294%) in urinary 8-OHdG.We didn't find significant associations between fine particulate matter (PM2.5) and urinary oxidative stress biomarkers.Conclusion: Our results suggested that exposure to air pollutants, especially UFP and PAHs, was responsible for exacerbation of systemic oxidative stress in COPD patients.Most air pollutants had stronger effects of systemic oxidative stress in mild to moderate COPD patients.