In the present prospective study, the Toll-like receptor 4 (TLR4) levels on peripheral blood mononuclear cells (PBMCs) were investigated in 30 patients with aneurysmal subarachnoid hemorrhage (aSAH) and in 20 healthy controls (HCs). The relationship between TLR4 levels and the occurrence of cerebral vasospasm (CVS) was also analyzed. TLR4 expression level on cell surface of PBMCs on days 1, 3, and 7 after admission was determined by flow cytometry. Results showed that patients with aSAH presented a significantly higher TLR4 levels. For patients with Hunt-Hess grades IV–V, higher TLR4 levels were also observed; higher TLR4 levels have already been seen in patients developing CVS and/or delayed cerebral ischemia (DCI). Higher TLR4 levels were also associated with modified Fisher score, occurrence of dCVS, DCI, cerebral infarction (CT), and poor neurological functional recovery. Binary logistic regression analysis indicated that high TLR4 expression on blood monocytes was an independent predictive factor of the occurrence of dCVS, DCI, and poor neurological functional recovery. Taken together, TLR4 levels on PBMCs is significantly altered in the early stage of aSAH, especially in those patients experiencing CVS and DCI. Furthermore, higher TLR4 levels in the early stage of aSAH is also associated with the neurological function outcome. As far as we know, this is the first clinical study about TLR4’s significance for patients with aSAH.