Bleeding risk is increased in patients with atrial fibrillation (AF) and moderate to severe kidney disease (KD); however, the implication of mild KD on bleeding remains unclear. The aim of this study was to determine whether the presence of mild KD increases risk for major bleeding (MB) in patients with AF undergoing percutaneous coronary intervention with stent implantation (PCI-S). Two hundred eighty-five patients were included. Patients were classified into three kidney function groups: moderate to severe KD (n=91; <60 ml/min/1.73 m²), mild KD (n=139; 60-89 ml/min/1.73 m²) and non-KD (n=55; ≥90 ml/min/1.73 m²). Estimated glomerular filtration rate was calculated using the simplified Modification of Diet in Renal Disease equation. Patients were followed for one year, and the occurrence of MB was obtained in all. A total of 28 patients (9.8%) presented MB. MB complications examined as a function of KD groups revealed that there was a graded increase in MB with worsening renal function (non KD=1.8%, mild KD=7.9%, moderate to severe KD=17.6%; p <0.001). Multivariable Cox regression analysis showed that mild KD was associated with nearly a 2.5-fold (2.43 95% confidence interval 1.11-5.34, p=0.039) increase in the risk of MB as compared with non-KD patients. Other independent predictors of MB were moderate-severe KD, anaemia and triple antithrombotic therapy after PCI-S (C-index=0.76). In this population, mild KD confers a significantly increase in the risk for MB complications. Future studies should assess the potential role of incorporating mild KD into the bleeding risk scales to improve the stratification of these patients.