Objective To investigate the predictive value of neutrophil to lymphocyte ratio (NLR) for the prognosis of patients with stroke warning syndrome (SWS). Methods From Jul. 2013 to Jan. 2020, 83 SWS patients admitted to The First Affiliated Hospital of Naval Medical University (Second Military Medical University) were retrospectively enrolled. According to the modified Rankin scale (mRS) score, the patients were divided into good prognosis group (mRS score≤2, n＝72) and poor prognosis group (mRS score＞2, n＝11). The clinical characteristics, laboratory data and imaging data were recorded, and the NLR was calculated according to the results of emergency blood routine test. Logistic regression model was used to analyze the influencing factors of poor prognosis of SWS patients. The receiver operating characteristic (ROC) curve was used to evaluate the predictive effect of NLR for the prognosis of SWS patients. Results The average age of SWS patients was (59.10±13.11) years old, and 65 patients had new cerebral infarction. Admission National Institutes of Health stroke scale (NIHSS) score and NLR of the patients in the poor prognosis group were significantly higher than those in the good prognosis group, while the hemoglobin level was significantly lower than that in the good prognosis group (all P＜0.05). There were no significant differences in ABCD2 (age, blood pressure, clinical features, duration of symptoms and diabetes) score, intravenous thrombolysis, or new infarction between the 2 groups (all P＞0.05). Multivariate logistic regression analysis showed that admission NIHSS score (odds ratio ［OR］ 1.46, 95% confidence interval ［CI］ 1.15-1.86, P＝0.002) and NLR (OR 2.05, 95% CI 1.07-3.92, P＝0.031) were independent risk factors for poor prognosis of SWS patients. ROC curve analysis showed a cutoff value of 2.82 for NLR in predicting poor prognosis in SWS patients, with a value of area under curve of 0.75, a sensitivity of 72.7%, and a specificity of 81.9%. Conclusion Higher admission NIHSS score and NLR are independently correlated with poor prognosis of SWS patients, and NLR has moderate diagnostic value for poor prognosis of SWS patients.