Proteinuria in kidney transplant recipients (KTRs) is associated with poor patient and allograft survival. However, the clinical relevance of spot urine protein to creatinine ratio (PCR) or albumin to creatinine ratio (ACR) during early postoperative period is yet to be determined. This single center retrospective cohort study included 474 KTRs who underwent kidney transplantation (KT) between 2014 and 2017. After excluding patients without urine PCR and ACR within 7 days after KT, 353 KTRs were included for analysis. PCR and ACR were measured during the immediate postoperative period (within postoperative 7 days), before discharge (postoperative 2 to 3 weeks), and at postoperative 3 to 6 months. The primary outcome and secondary outcomes were the estimated glomerular filtration rate (eGFR) at postoperative 1 year and the incidence of delayed graft function (DGF), respectively. KTRs with higher PCR (β coefficient = -8.66, p = 0.01) or ACR (β coefficient = -6.97, p < 0.001) at postoperative 3 to 6 months showed lower eGFR at postoperative 1 year after adjusting for sex, age, donor status, and acute rejection withing 3 months using multivariable analysis. DDKT recipients with immediate postoperative PCR ≥ 3 mg/mg showed higher incidence of DGF (PCR < 3 mg/mg vs. PCR ≥ 3 mg/mg, 12% vs. 39%; p < 0.001) and lower eGFR before discharge (64.2 [49.7 - 85.4] vs. 49.6 [35.8 - 66.5]; p = 0.001) compared to KTRs with immediate postoperative PCR < 3 mg/mg. Proteinuria at postoperative 3 to 6 months seems to be a potential predictor of early renal outcome in KTRs, and heavy proteinuria (PCR ≥ 3mg/mg) during the immediate postoperative period may be a potential predictor of DGF in DDKT recipients. Our study suggests that early postoperative proteinuria may be a useful biomarker for predicting early renal outcome after KT.