Background: Despite the fact that the monocyte count/HDL-C ratio (MHR) has been studied extensively in patients with chronic kidney disease as an independent predictor of both fatal and composite cardiovascular events. Only a few studies have looked at the MHR in patients with non-ST elevation acute coronary syndrome (NST-ACS). Objective: Using the SYNTAX score (SX score) in patients with non-NST-ACS, we will undertake this study to examine MHR as an independent predictor of the complexity and severity of coronary atherosclerosis. Subjects and methods: This study was a cohort analytical retrospective study conducted on 156 patients presented with NST-ACS admitted for coronary angiography, collected from Zagazig Catheterization Laboratory Database. All patients had the following: Cardiac enzymes, complete blood count, lipid profile and serum creatinine. The SX score was determined with baseline coronary angiography Results: Patients were divided into two groups based on their Syntax score: Group 1 (score < 23) and group 2 (Score > 23). There was significant positive correlation between monocyte/HDL-C ratio and SYNTAX score (p=0.001) with correlation coefficient 0.768. Receiver operating characteristic (ROC) curve showed that the best cutoff value for monocyte/HDL-C ratio for prediction of the severity of coronary artery disease assessed by SYNTAX score in the studied population was 22.25 with area under the curve (AUC): 0.975, sensitivity of 95% and specificity of 75%, (p value 0.0001). In-hospital non-fatal MI was higher among patients with high MHR (P: 0.029), but no statistically significant difference between both groups of MHR regarding in-hospital, 3 months CV mortality and 3 months non-fatal MI was revealed. Conclusion: MHR as a novel inflammatory marker is indicated to be an independent predictor of severity of coronary artery disease among patients presenting with NST-ACS.