More and more evidence shows that microRNAs (miRNAs) play an important role in the diagnosis and prognosis of human diseases. In this study, we investigated the diagnostic value of miR-9-5p for asymptomatic carotid artery stenosis (CAS) and its predictive value for future cerebrovascular events within 5 years. A total of 88 asymptomatic CAS patients and 86 healthy individuals were recruited. The expression level of serum miR-9-5p was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The diagnostic value of miR-9-5p in CAS was assessed by a receiving operator characteristic (ROC) curve. The predictive value of miR-9-5p for the occurrence of cerebrovascular events was evaluated by the Kaplan-Meier method. The serum level of miR-9-5p was significantly decreased in asymptomatic CAS patients. ROC curve had an AUC value of 0.910, with the sensitivity and specificity of 80.7% and 87.2% at the cut-off value of 0.72, respectively. A total of 25 patients had cerebrovascular events during the 5-year follow-up, including 3 strokes and 22 transient ischemic attacks (TIAs). Kaplan-Meier survival analysis revealed that the low expression level of miR-9-5p was an independent factor closely related to the occurrence of cerebrovascular events. Serum miR-9-5p could be used as a new biomarker for the diagnosis of CAS, and the low expression of miR-9-5p is associated with poor prognosis.