Glomerular IgG deposition is frequently observed in patients with IgA nephropathy. However, the association between glomerular IgG deposition and progression of IgA nephropathy is uncertain. Six hundred and twenty-seven patients with biopsy-proven IgA nephropathy were recruited. Histological variables of the Oxford classification (Oxford-MEST) and the presence of glomerular IgG deposits were assessed. Renal progression defined as end-stage renal disease or 50% reduction in estimated glomerular filtration rate was analyzed using Kaplan-Meier methods and Cox regression analysis. Of the study population, 200 patients (31.9%) had glomerular IgG deposition on immunofluorescence staining. During a mean follow-up of 56.8±37.5 months, the rate of renal progression was significantly higher in the IgA nephropathy patients with glomerular IgG deposition compared with the IgA nephropathy patients without glomerular IgG deposition (39.8 vs 12.3 per 1000 patient-years; P<0.001). Of patients with IgG deposition, 178 (28.3%), 20 (3.2%), and 2 (0.3%) patients had mild, moderate, and marked glomerular IgG deposits, receptively. Kaplan-Meier analysis revealed that cumulative renal survival was significantly lower in IgA nephropathy patients with the higher intensity of glomerular IgG deposits (P<0.001). In addition, Cox regression analysis revealed that moderate and marked glomerular IgG deposits significantly predicted renal outcome independent of Oxford-MEST and clinical variables (HR, 2.97; 95% CI, 1.01-8.77; P=0.04). This study showed that that glomerular IgG deposition was independently associated with poor renal outcome in patient with IgA nephropathy.