Objective: Our aim in this study was to investigate the relationship between coronary artery disease severity and basophil ratio in pa-tients without ST segment elevation myocardial infarction. Material and Method: We included patients who have been diagnosed with ST segment elevation myocardial infarction in the emer-gency department within the past year. These patients were performed coronary angiography and had at least one vessel had 50% stenosis. Venous blood was taken at the time of admission. Renal function, lipid parameters and complete blood count were studied. Two cardiologists evaluated the images of coronary angiography, independently of each other. Syntax score was calculated by including vessels with vessel diameters greater than 1.5 mm and vessels with more than 50% stenosis. The patients were divided into two groups: group 1 (middle-low risk, Syntax Score <17) and group 2 (high risk, syntax score ≥17). Results: We included 279 patients (mean age 64.1±12.3 years) in our study. In the group 1, total protein, albumin, triglyceride, hemo-globin, lymphocyte, and basophil ratio were significantly higher than group 2 (p values respectively; 0.017, 0.041, 0.011, 0.008, 0.001 and 0.001). In the group 2; age, neutrophil, neutrophil / lymphocyte ratio, significantly higher than group 1 (p values respectively; <0.001, 0.002, 0.001). Multiple logistic regression analysis was performed with variables with p <0.05 to determine independent mark-ers for syntax score. The age (OR: 1.033, 95% CI: 1.006 - 1.061, p=0.017) and basophil ratio (OR: 0.981, 95% CI:0.967-0.995, p=0.008). Conclusion: If the basophil ratio is low, coronary artery disease extensity and severity tend to increase in patients with ST segment ele-vation myocardial infarction.