Background : Coronary artery diseases are the predominant cause of morbidity and mortality in developed and developing countries. Thus, extraordinary efforts have been directed to determine the molecular and pathological characteristics of the diseased heart ,in order to develop novel diagnostic and therapeutic strategies .miRNAs are class of abundant, non-coding RNAs that attracted scientists′ attention for their promising role as diagnostic and prognostic biomarkers in cardiovascular diseases. Aim of the work: To identify whether miRNA-1 is a dependable biomarker for diagnosis of acute myocardial infarction or not. Subjects and methods: 69 patients with coronary artery disease were included in this study; 36 patients with AMI and 33 patients with unstable angina. Those patients were admitted to coronary care unit, Assuit University Hospital during the period of March to October 2014. In addition to, 22 apparently healthy subjects were included as a control group. Cardiac troponin I & miRNA-1was done for all subjects. Results: In patients with AMI the results of miRNA-1 ranged from 28.3 – 6763.9 fold changes above the control level. In those with UA, miRNA-1 result ranged from 1.74 – 144.37 fold changes above the control level (when the control group is one fold). Comparison between different groups regarding results of miRNA-1 revealed that there was a highly significant difference (P<0.001) between different groups. There was a highly significant increase in patients with AMI when compared with the control group, also a statistically significant increase (P<0.001) in patients with UA when compared with the control group and a statistically significant increase (P<0.001) in patients with AMI when compared with those of UA. Conclusion: miRNA-1 is a novel dependable biomarker in patients with acute coronary syndrome. It shows significant upregulation in patients with AMI, but this upregulation is far from that of UA.