The aim of the present study was to determine whether urinary 8-hydroxydeoxyguanosine (8-OHdG), which is a marker of oxidative stress, can predict future cardiovascular death in patients with acute coronary syndrome (ACS). A total of 551 consecutive patients with ACS who underwent admission urinary 8-OHdG measurements were enrolled in this study. The patients were divided into 2 groups according to the optimal cutoff value of admission urinary 8-OHdG determined by a receiver-operating characteristics curve for the prediction of cardiovascular death: a high admission urinary 8-OHdG group, 169 patients with admission urinary 8-OHdG ≥ 17.92 ng/mg creatinine; and a low admission urinary 8-OHdG group, 382 patients with admission urinary 8-OHdG < 17.92 ng/mg creatinine. The patients were followed up for a median period of 34 months. The primary and secondary end points were the incidence of cardiovascular death and major cardiovascular events (MACE) composed of cardiovascular death, non-fatal myocardial infarction, or urgent hospitalization for heart failure. Of the 551 patients, cardiovascular deaths and MACE occurred in 14 (2.5%) and 35 (6.4%), respectively. The Kaplan–Meier estimate of the event-free rate revealed cardiovascular deaths and MACE were more likely in the high admission 8-OHdG group than in the low admission 8-OHdG group (log rank, both P < 0.001). Multiple adjusted Cox proportional hazards analysis indicated that high admission urinary 8-OHdG was an independent predictor of cardiovascular death (hazard ratio [HR] 7.642, P = 0.011) and MACE (HR 2.153, P = 0.049). High admission urinary 8-OHdG levels predict cardiovascular mortality after adjustment in patients with ACS.