Objective: This work studied platelet-neutrophil aggregates (PNA) expression in patients with acute ST-segment elevation myocardial infarction (STEMI). Methods: Our research included in 2 groups: STEMI group, n=40 patients admitted in our hospital and Control group, n=30 normal subjects. Blood levels of PNA, platelet-monocyte aggregates (PMA) and platelet-lymphocyte aggregates (PlyA) were measured by lfow cytometry at admission and the results were compared between 2 groups. Results: Compared with Control group, STEMI group had similar blood levels of PlyA and PMA,P=0.245 andP=0.312; while increased blood level of PNA,P<0.05. Correlation analysis showed that platelet-leukocyte aggregates (PLA) level was positively related to CK-MB (r=0.4992,P<0.01) and cTnI (r=0.4365,P<0.01). Conclusion: Blood level of PLA, especially PNA was significantly higher in STEMI patients which suggested that increased PNA might be sued as a new index for AMI diagnosis in clinical practice.