Objectives: The elderly population is increasing worldwide, and the risk of obesity and related diseases also increases with age. Old age and obesity are important risk factors for chronic kidney disease (CKD), but studies on obesity and renal dysfunction in the elderly are still lacking. Therefore, we evaluated the association between obesity and renal outcomes. Methods:  To determine the association of obesity with renal outcomes we used data in the geriatric cohort database of the NHIS. Obesity was classified according to body mass index (BMI), sex-specific waist circumference (WC) quartiles, and metabolic syndrome. Renal composite outcome was defined as a worsening kidney function as sustained decline in the eGFR of at least 50%, or end stage renal disease. Incident CKD was defined as the decline of eGFR below 60 ml/min/1.73m2 at follow up. Results: Of the 130,504 participants, worsening kidney function occurred in 19.0%. Multivariate Cox regression analysis revealed that the risk of renal composite outcome was not associated with BMI or WC. On the other hand, the group with metabolic syndrome had a significantly higher risk of renal composite outcome than the group without metabolic syndrome. In addition, the risk of renal composite outcome increased significantly as the number of components increased. In subgroup analysis with participants with baseline eGFR ≥60 ml/min/1.73m2, incident CKD was associated with high WC and the presence of metabolic syndrome. Conclusions: In a nationwide cohort of the elderly Korean adults, the presence of metabolic syndrome rather than BMI or WC was associated with increased risk of renal function decline, and WC and metabolic syndrome were associated with increased risk of incident CKD.