Background: Mean platelet volume (MPV), is an indicator of platelet reactivity and could be a biomarker of the risk and prognosis of patients with ST-segment elevation myocardial infarction (STEMI). Objectives: Testing the predictive value of MPV for angiographic thrombus burden and short-term outcomes in patients with STEMI undergoing primary percutaneous coronary intervention (PPCI). Patients and Methods: Seventy-two patients presented with acute STEMI to the Cardiology Department of Ain Shams University Hospitals for PPCI. MPV was measured on admission. Angiographic thrombus burden and post-interventional thrombolysis in myocardial infarction (TIMI) flow grade and myocardial blush grade (MBG) were recorded. Patients were followed up for 3 to 6 months. Results: The patients' ages ranged between 33 and 73 (mean age 53.22 ± 9.96 years). This study included 62 males and 10 females. The MPV of the studied cases was 9.97 ± 1.31 fl. MPV was higher among patients with high thrombus burden (HTB) (11.42±1.007 vs. 9.53±1.039. p < 0.001) and patients with MBG (0-1) and TIMI flow>3 (10.59±1.839 vs 9.81±1.092, p 0.04 and 11.77±0.74 vs 9.87±1.26, p 0.004 respectively). The primary composite endpoint occurred in 12 patients with a higher MPV (10.95 ± 1.14 vs. 9.73 ± 1.29, p 0.01). In univariate regression analysis for the predictors of MBG (0/1), the MPV was an independent predictor of MBG (odds ratio 0.487, and p <0.006), CI (0.292- 0.811). Conclusion: MPV may be a useful biomarker to help identify higher-risk patients with large intracoronary thrombus burden, who might require more potent antiplatelet therapy.