Abstract Funding Acknowledgements Type of funding sources: None. Objective The pathophysiology of carotid artery stenosis (CAD) is not fully understood. Research has shown that mean platelet volume (MPV) is a potential marker for platelet activation and a key factor in the pathophysiology of atherosclerosis. Recently, the ratio of monocyte count to HDL (MHR) has been identified as a predictor of cardiovascular events in patients. In the light of these findings, the goal of this study was to evaluate the potential association of MPV and MHR with the severity of CAD. Material-Method The patients were divided into three groups: CAD≥ 60% (40 patients), CAD <60% (40 patients) and no carotid atherosclerotic disease (40 individuals). Patients' demographic characteristics, clinical features and laboratory findings were compared between the groups. Results MPV and MHR levels were lower in the control group than CAD <60 group and lower in CAD <60 group than CAD ≥60 group (p <0.001, p <0.001). Higher MPV (OR= 6.050; 95% CI: 2.946-12.427; p <0.001) and MHR (OR= 1.107; 95% CI: 1.045-1.159; p <0.001) levels were detected as an independent predictor for ≥60% carotid artery stenosis after multiple linear regression analysis. In the correlation analysis, a positive correlation was found between MPV and the rate of carotid artery stenosis (p<0.001, r=0.680). Conclusion In our study, a potential relationship between MPV and MHR with carotid artery disease was determined. Our study may make contributions to understanding the pathophysiology of carotid artery atherosclerosis and developing treatments for it.