The preservation of kidney function after kidney donation depends on the kidney reserve - the potential of the remaining kidney to boost their function after loss of the other kidney. In Traditional Chinese Medicine, size and shape of the external ears are examined to evaluate the person's kidney health. We hypothesized that ear size might be a practical yet overlooked marker of kidney reserve. Fifty kidney transplantation donors were participated in this study. The length and width of both ears of all participants were measured during one of the post-donation visits. Pre-donation serum creatinine and post-donation serum creatinine as well as other relevant parameters (age, sex, weight, height, etc.) of the participants were extracted from medical records. The estimated GFR was calculated from serum creatinine, age and sex using the CKD-EPI equation. Ear length negatively associated with % GFR decline after kidney donation. For every 1 cmincrease in ear length, it was associated with 5.7% less GFR decline after kidney donation (95% Confidence Interval 0.2 to 11.3, P=0.04). Earwidth, aswell as age, sex, bodyweight, height, body mass index, and pre-donation eGFR did not significantly associate with the GFR decline. Our findings support the notion of Traditional Chinese Medicine that ear morphology may be associated with kidney health and suggest that ear lengthmight be a useful predictor of kidney function decline after kidney donation.