Objectives: Causes of persistent proteinuria are diverse, usually indicating a disease of the urinary system. If left untreated, proteinuria may contribute to kidney damage through various mechanisms including oxidative stress and inflammation. Therefore, persistent proteinuria mandates investigation and intervention. In asymptomatic children, at first orthostatic proteinuria or tubular proteinuria is suspected. Upon excluding these, a kidney biopsy is considered to rule out glomerulopathy. However, sometimes histology turns out to be non-specific. The recent discovery of CUBN, encoding the membrane glycoprotein cubilin, sheds light on some of those cases. Since cubilin is a component of the cubilin-amnionless-megalin complex that is responsible for the receptor-mediated endocytosis of albumin in the proximal tubules, a defect of cubilin leads to a reduction in albumin reuptake, consequently results in albumin-dominant proteinuria. This research is to identify CUBN mutations causing benign isolated proteinuria. Methods: Children with proteinuria without nephrotic syndrome feature (edema, decreased serum albumin levels ) were selected to get WES (IRB No: 2011-048-1171). Retrospectively, five cases (M;F 3;2) with persistent proteinuria associated with homozygous or compound heterozygous C-terminal variants of CUBN were selected for analysis.  Results: All patients presented with incidentally found isolated asymptomatic proteinuria, at their median age of 7 years (range 1.5 ~ 9). Their urine protein creatinine ratios were median 0.84 (0.57 ~ 2.03) mg/mg at presentation and did not change significantly over time regardless of RAS inhibition (median follow-up duration of 4 years [1 yrs~12yrs]). Their laboratory findings were also unremarkable at presentation or during follow-up for estimated GFR, serum albumin, lipid, hemoglobin, urine b2-microglobulin. None had hypertension, and kidney ultrasound showed normal kidneys. Among two patients, a kidney biopsy was done, which revealed no remarkable findings. Conclusions: These cases are similar to previously reported cases, indicating benign proteinuria associated with C-terminal variants of CUBN needs to be considered in such cases.