Objective: To explore the expression changes of serum interleukin（IL）9 level in patients with acute cerebral infarction and evaluate its value. Methods: 106 patients with cerebral infarction were collected. According to whether or not early neurological deterioration （END） occurred, the patients with cerebral infarction were divided into END group （42 cases） and non-END group （64 cases）. The general data of patients with cerebral infarction were collected, and the National Institute of Health stroke scale （NIHSS） score was recorded, and serum biochemical indices, serum IL-9, C-reactive protein （CRP） and IL-6 levels at baseline were detected. Pearson or Spearman correlation analysis was used to evaluate the correlation. Logistic regression was used to analyze the factors affecting the occurrence of END in patients with cerebral infarction, and ROC curve was drawn to evaluate the predictive value of serum IL-9 level in the occurrence of END of cerebral infarction. Results: The proportion of diabetes mellitus, carotid artery stenosis>50%, low density lipoprotein, glycosylated hemoglobin and NIHSS score at admission in END group were all higher than those in non-END group （P<0.05）. The level of serum IL-9 in the END group was significantly higher than that in the non-END group （P<0.01）. The level of serum IL-9 in patients with cerebral infarction was positively correlated with NIHSS score at admission （r=0.535, P<0.01）. Logistic regression showed that serum IL-9 level, carotid artery stenosis > 50% and NIHSS score at admission were risk factors for END （P<0.01）. The area under ROC curve of serum IL-9 level predicting END occurrence was 0.815. Serum IL-9 level was positively correlated with serum CRP level （r=0.648, P<0.01） and serum IL-6 level （r=0.765, P<0.01）, respectively. Conclusion: Serum IL-9 level is significantly increased in patients with cerebral infarction END, which has a good predictive effect on the occurrence of END.