Purpose: To evaluate the effect of partial nephrectomy on renal function and to identify predictors of estimated glomerular filtration rate (eGFR) at six months after partial nephrectomy. Methods: Medical data of 154 consecutive patients who underwent partial nephrectomy for a renal mass between January 2015 and March 2020 were retrospectively analyzed. The primary outcome measure was eGFR at six months postoperatively. A non-linear regression analysis was performed to examine the association between primary outcome measure and candidate predictors. Results: Of the patients, 66 (42.9%) were females and 88 (57.1%) were males with a median age of 60 (range, 50 to 67) years. The median baseline eGFR was 90.40 (range, 74.96 to 102.97) mL/min/1.73 m2, while the median eGFR at six months was 77.12 (range, 61.06 to 91.93) mL/min/1.73 m2 (p<0.001). Baseline eGFR (=22.691, 95%CI: 18.821 to 26.460, when baseline eGFR levels change from 74.97 ml/min/1.73 m2 to 102.68 ml/min/1.73 m2, p<0.001) was found to be directly associated with the postoperative eGFR levels at six months. In contrary, advanced tumor size (=-3.168, 95%CI: -5.332 to -1.005, when tumor size levels change from 3 to 6 cm, p<0.001) and presence of hypertension ( = -3.479, 95%CI: -6.956 to -0.0031, p=0.049) were also found to be inversely associated with the postoperative eGFR levels at six months. Conclusion: Baseline eGFR values, tumor size, and presence of hypertension are significant predictors of eGFR values in the mid-term in patients undergoing partial nephrectomy.