Background Macrophages in atherosclerotic plaques secrete YKL-40, a new biomarker of acute and chronic inflammation in patients with stable CAD. We hypothesized that YKL-40 may be a specific marker reflecting the burden of localized inflammation in myocardium and a predictor in patients with STEMI. In this study, we investigated the relationship of YKL-40 to in-hospital major adverse cardiac events (MACE), reperfusion parameters and its predictors in patients with STEMI. Methods In total, 80 patients with STEMI and no history of prior coronary artery disease (CAD), who underwent primary percutaneous coronary intervention (p-PCI), were enrolled consecutively. In addition, 30 patients with normal coronary arteries (NCA) were enrolled as a control group. Cardiac biomarker levels including creatinine kinase-MB fraction (CK-MB), troponin-I, admission glucose and inflammatory markers including leukocytes and YKL-40 levels were measured as admission values. Results In our study, YKL-40 levels correlated to high-sensitivity CRP levels ( r  = 0.333, p  = 0.003), TIMI risk score ( r  = 0.445, p  < 0.001), age ( r  = 0.477, p  < 0.001), pain to balloon time ( r  = 0.432, p  < 0.001), leukocyte and neutrophil count ( r  = 0.386, p  < 0.001 and r  = 0.430, p  < 0.001, respectively), hemoglobin ( r  = − 0.345, p  = 0.002), admission and fasting blood glucose ( r  = 0.388, p  < 0.001 and r  = 0.427, p  < 0.001), creatinine levels ( r  = 0.395, p  < 0.001) and myocardial blush grade ( r  = − 0.334, p  = 0.004). When the patients were divided into two groups determined by presence or absence of MACE, the patients with MACE had significantly higher levels of YKL-40 in comparison to the patients without MACE and the control group (194 ± 104, 114 ± 61 and 110 ± 53 μg/L, p  < 0.001, respectively). In multivariate logistic regression analysis in STEMI patients, only YKL-40 level (OR: 1.011, 95%CI: 1.002–1.019, p  = 0.011) and leukocyte count (OR: 1.264, 95%CI: 1.037–1.540, p  = 0.020) were the independent predictors for MACE. Sensitivity and specificity of YKL-40 to predict MACE, when 125 μg/l was accepted as a cut-off value, were 84% and 70%, respectively. Conclusion We found that serum YKL-40 is related to older age, increased admission glucose levels, leukocyte counts and decreased hemoglobin levels; YKL-40 level and leukocyte count independently predicted MACE.