Objective To explore the relationship between neutrophil-lymphocyte ratio (NLR) and the short-term prognosis of elderly patients with acute coronary syndrome (ACS). Methods The clinical data of elderly ACS patients, who were hospitalized at Department of Cardiology of Zhongda Hospital Southeast University from Jan. 2015 to Oct. 2017, were retrospectively analyzed. All patients were diagnosed by coronary angiography in combination with clinical symptoms, myocardial necrosis markers and electrocardiogram. According to NLR detected immediately after admission (within 4 h), 500 elderly ACS patients were divided into 3 groups:NLR ≤ 3.337 group (n=169), NLR 3.338-6.166 group (n=167), and NLR ≥ 6.167 group (n=164). The primary endpoints of the study were all-cause deaths during hospitalization and follow-up. The secondary outcomes were major adverse cardio-cerebrovascular events (MACCEs), hospital stay and left ventricular ejection fraction (LVEF). Results In NLR ≤ 3.337 group, NLR 3.338-6.166 group and NLR ≥ 6.167 group, the hospital stays were 8 (6, 11) d, 9 (7, 11) d and 10 (8, 11) d, the incidence rates of LVEF<50% during hospitalization were 8.9% (15/169), 14.4% (24/167) and 18.3% (30/164), and the LVEF values were (57.78±12.15)%, (54.71±11.73)% and (53.56±13.38)%, respectively, and the differences among three groups were significant (all P<0.05). The incidence of MACCEs was 21.6% (108/500) during hospitalization. Six patients died during a follow-up period of 6 months after discharge. There were no significant differences in all-cause mortality or MACCE incidence among three groups (both P>0.05). Multivariate Cox risk regression model showed that there was no association between NLR and all-cause death, MACCEs, cardiogenic death, myocardial infarction, or stroke (all P>0.05). Compared with the NLR ≤ 3.337 group, the incidence rates of LVEF<50% during hospitalization were significantly increased in the NLR 3.338-6.166 group (hazard ratio[HR]=2.567, 95% confidence interval[CI] 1.558-4.229, P<0.001) and the NLR ≥ 6.167 group (HR=1.979, 95% CI 1.629-3.524, P=0.019). Reciever operating characteristic curve showed that area under curve of NLR in evaluating LVEF<50% during hospitalization was 0.652 (95% CI 0.603-0.700, P<0.001). The optimal cut-off value of NLR was 3.84, and the sensitivity and specificity were 68.3% and 65.3%, respectively. The multiple linear regression model showed that high NLR was an independent influencing factor of prolonged hospital stay (β=0.181, P<0.001). Conclusion In elderly ACS patients, NLR is a risk factor of LVEF<50% during hospitalization and prolonged hospital stay, while it has no significant association with all-cause death and MACCEs.