Objectives: We sought to assess the impact of clopidogrel loading dose in patients with chronic kidney disease (CKD) undergoing primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI). Background: CKD is associated with worse prognosis and increased bleeding risk in patients with acute myocardial infarction. A 600 mg loading dose of clopidogrel compared with 300 mg provides a more rapid and greater degree of platelet inhibition. Methods: Using the Korea Acute Myocardial Infarction Registry (KAMIR), a total of 1,457 patients with CKD (estimated glomerular filtration rate < 60 ml/min/1.73m2) undergoing primary PCI for STEMI were evaluated according to clopidogrel loading dose: high loading dose group (600 mg, n = 861) versus standard loading dose group (300 mg, n = 596). We compared in-hospital complications including major bleeding and clinical outcomes at 1-month and 12-months between the 2 groups. Results: Between the 600 mg and 300 mg clopidogrel loading dose groups, in-hospital major bleeding rate was similar (0.8 % vs. 0.2 %, p = 0.09). Also, there were no differences in major adverse cardiac events (MACEs) rates including death, recurrent myocardial infarction, repeated PCI and stent thrombosis at 1-month (15.6 % vs. 16.4 %, p = 0.70) and 12-months (19.0 % vs. 21.3 %, p = 0.32). By multivariate analysis, 600 mg loading dose of clopidogrel was not an independent predictor of 1-month (OR 1.13, 95 % CI 0.49-2.57, p = 0.78) and 12-months MACEs (OR 0.89, 95 % CI 0.52-1.51, p = 0.66). After propensity score matched analysis, these results were unchanged. Conclusions: A 600 mg loading dose of clopidogrel was not effective reducing the both 1-month and 12-months MACEs in patients with CKD undergoing primary PCI for STEMI but did not increase in-hospital major bleeding rate.