Purpose We evaluated the factors affecting changes in the postoperative glomerular filtration rate (GFR) after unilateral nephrectomy in living kidney donors and patients with renal disease. Methods We studied 141 subjects who underwent living donor nephrectomy for renal transplantation (n=75) or unilateral nephrectomy for renal diseases (n=66). The GFR of the individual kidney was determined by Tc-99m DTPA scintigraphy before and after nephrectomy. By performing multiple linear regression analysis, we evaluated the factors that are thought to affect changes in GFR, such as age, sex, body mass index (BMI), preoperative GFR, preoperative creatinine level, operated side, presence of diabetes mellitus (DM), presence of hypertension (HTN), and duration of follow-up. Results In both the donor nephrectomy and the disease nephrectomy groups, GFR increased significantly after nephrectomy ($46.9{pm}8.4$ to $58.1{pm}12.5$ vs. $43.0{pm}9.6$ to $48.6{pm}12.8$ ml/min, p<0.05). In the donor nephrectomy group, age was significantly associated with change in GFR (${eta}$=-0.3, p<0.005). In the disease nephrectomy group, HTN, preoperative creatinine level, and age were significantly associated with change in GFR (${eta}$=-6.2, p<0.005; ${eta}$=-10.9, p<0.01; ${eta}$=-0.2, p<0.01, respectively). This compensatory change in GFR was not significantly related to sex, duration of follow-up, or operated side in either group. Conclusions The compensatory change in the GFR of the remaining kidney declined with increasing age in both living kidney donors and patients with renal disease.