Obesity is a risk factor for chronic kidney disease, and its prevalence among the elderly is increasing. We investigated the effects of changes in body fat percentage (BFP) on the longitudinal changes in the estimated glomerular filtration rate (eGFR) in the elderly. This prospective cohort study included 390 participants aged >65 years who underwent bioelectrical impedance analysis at baseline and follow-up as a part of the Korean Longitudinal Study on Health and Aging. After a median follow-up period of 5.3 years, BFP was significantly higher than that at the start point (P<0.05). Participants who had the largest increase in BFP had the highest BMI and waist circumference (WC) (P<0.001). The highest tertile had the highest white blood cell count and erythrocyte sedimentation rate, incidence of rapid progression, and decline in eGFR >25% (P≤0.017, P = 0.025, P = 0.005, respectively). The lowest tertile had the lowest triglyceride and highest high-density lipoprotein levels (P<0.05). The adjusted decline rate in eGFR was correlated with a change in BFP (P = 0.039), but not with that in BMI or WC. The highest tertile had a 4.875-fold increase in the risk for rapid progression to a decline in eGFR (95% CI: 1.366-17.397) and a 4.931-fold decrease in the risk to a decline in eGFR>25% (95% CI: 1.617-15.037), when compared with the lowest tertile. In subgroup analysis, the incidence of renal outcomes was significantly increased according to the increase in BFP in patients with lower eGFR (P≤0.010). A change in BFP may be associated with inflammation and dyslipidemia development, and longitudinal changes in body fat are related to a decrease in eGFR in the elderly.