An equation for the estimated glomerular filtration rate (eGFR) is generally used for evaluating renal function in Japan.To assess the accuracy of the preoperative eGFR for estimating kidney donors' measured glomerular filtration rate (mGFR).Between April 2009 and August 2014, 91 Japanese living kidney donors were included in this study. The eGFR was calculated as follows: eGFR = 194 × serum creatinine(-1.094) × Age(-0.287) (and × 0.739 for women), and the mGFR was evaluated using inulin clearance. The preoperative eGFR was then compared with the mGFR.Patients included 27 men and 64 women with a mean age of 56.8 ± 9.5 years (range, 36-79 years), mean body surface area of 1.56 ± 0.14 m(2) (range 1.27-1.92 m(2)), mean body mass index of 22.3 ± 2.3 kg/m(2) (range 14.0-27.0 kg/m(2)), and mean serum creatinine level of 0.66 ± 0.14 mg/dL (range 0.39-0.97 mg/dL). The mean eGFR was 81.3 ± 14.2 mL/min/1.73 m(2) (range 45.5-125.9 mL/min/1.73 m(2)), and the mean mGFR was 89.0 ± 15.5 mL/min/1.73 m(2) (range 45.4-130.7 mL/min/1.73 m(2)). The eGFR was significantly lower than the mGFR (P < .001). The correlation coefficient for the relationship between the eGFR and mGFR values was 0.503, and the mean difference between the 2 values was -7.8 (8.7%).Although the eGFR correlated with the mGFR, the eGFR values did not accurately estimate the mGFR in living kidney donors. Therefore, it is necessary to evaluate the mGFR, especially in marginal kidney donors.