The introduction: The early diagnosis and exclusion of acute coronary syndrome is still challenging, that requires monitoring of the patients and serial measurements of cardiac biomarker (Hs-c-TnsI). The addition of cardiac biomarker (serum Copeptin) may reflect the early ischemic cardiac injury. We aimed for detection the diagnostic value of serum copeptin level and its role in prediction of short-term outcomes; MACCE in ACS patients as a new cardiac biomarker. Subjects and methods: We included ninety patients attended an emergency cardiac care department due to acute chest pain (within less than three hours from onset of the chest pain) and divided into ; the 1st group included forty patients (acute STEMI who successfully received primary PCI). The 2nd group included fifty Patients (other diagnosis; (non-AMI)). The study endpoint was (MACCE). The patients were subjected to the full laboratory profile (CBC, kidney function tests, total CK, CK- MB, highly sensitive Cardiac Troponin I, serum Copeptin) . Results: The ROC analysis showed that At AUC of 0.891 and cut off value of >12.4 pmol/l, copeptin had a sensitivity of 75 % ,specificity 92 %, PPV 88.2 % ,NPV 82.1 % and accuracy 84.4 % in early diagnosis of acute MI. There was statistical significance of serum Copeptin level that correlated with (CK-MB and hs-cTnI ). In conclusion, our study revealed that Copeptin can early diagnose acute myocardial infarction but not superior to highly sensitive troponin. Higher serum copeptin levels were independent prognostic predictors of MACCE in acute MI patients during short-term follow up