This study aimed to evaluate the relationship between no-reflow phenomenon and systemic inflammation index (SII) and to compare the predictive capacity of SII together with the neutrophil–lymphocyte ratio (NLR), and the platelet–lymphocyte ratio (PLR) in patients with ST-elevation myocardial infarction (STEMI). A total of 785 patients were included. The thrombolysis in myocardial infarction (TIMI) flow degree has been used to describe the no-reflow phenomenon. The study population was divided into two groups regarding the presence of no-reflow phenomenon including 110 patients with no-reflow (TIMI frame count 0-2) and 675 patients without no-reflow (TIMI frame count 3). The NLR [6.6 (4.6-11.6) vs 3.2 (2.0-5.3); P < .001], PLR [175 (121.3-220) vs 102.6 (76.1-150.1); P < .001] and SII [1921(1225-2906) vs 738.5 (450.5-1293); P < .001] were significantly higher in the no-reflow group. High NLR (OR: 1.078, 95%CI: 1.027-1.397; P = .021), PLR (OR: 1.009, 95%CI: 1.003-1.021; P = .041) and SII (OR: 1.216, 95%CI: 1.106-1.942; P = .004) were found to be independently associated with no-reflow phenomenon. The comparison of the receiver-operating characteristic curves showed that area under the curve of SII was greater than that of NLR (.789 vs .766, P = .007) and PLR (.789 vs .759, P = .048). SII levels may predict no-reflow phenomenon better than NLR and PLR.