To assess the value of monitoring cerebral vascular reactivity (CVR) and microembolic signal (MES) by transcranial doppler (TCD) in patients with internal carotid artery (ICA) stenosis. Methods: We recruited 92 patients with ICA ≥50% to the study. Based on the presence of clinical symptoms, patients were placed into the symptomatic group (55 patients) or asymptomatic group (37 patients). The degree of stenosis, atherosclerotic plaque morphology, vascular motor reactivity (VMR), cerebrovascular reserve capacity (CRC), breath holding index (BHI), and MES monitoring were assessed by TCD. Based on TCD results, patients were divided into the 50%-69% ICA stenosis group and ≥70% ICA stenosis group; according to the plaque grey-scale median (GSM), they were divided into the hypoechogenic (GSM≤25) plaque group and hyperechogenic (GSM＞25) plaque group; based on ulceration on plaques, they were divided into the ulcerated plaque group and non-ulcerated plaque group. Results: In the symptomatic group, ≥70% ICA stenosis and ulcerated plaques occurred significantly more often than in the asymptomatic group (both P＜0.01). MES were recorded significantly more often in the symptomatic, ≥70% ICA stenosis, ulcerated plaque, and hypoechogenic plaque groups compared to that in the asymptomatic, 50%-69% ICA stenosis, non-ulcerated plaque, and hyperechogenic plaque groups, respectively (all P<0.05). VMR and CRC in the symptomatic group were significantly lower than that in the asymptomatic group (both P＜0.05). VMR, CRC, and BHI in the ≥70% ICA stenosis group were significantly lower than that in the 50%-69% ICA stenosis group (all P＜0.05). Conclusion: In patients with symptomatic ICA, MES are one of the ultrasound features of unstable carotid stenosis. CVR decrease is related to the degree of ICA stenosis and the presence of clinical symptoms.