Background: The ratio of urine protein to urine osmolality has recently been suggested as an accurate method to determine proteinuria. Objective: We studied the correlation of urine protein to urine osmolality ratio with 24-hr urinary protein excretion. Methods: 150 children aged 0.11–17 years admitted to the Department of Pediatric Nephrology were included in this study. Early morning urine samples and 24-hr urine specimens were collected and analyzed for protein, creatinine, and osmolality. The patients with chronic renal failure were not excluded. Two groups were established: Children with no proteinuria (group 1) and those with proteinuria (group 2). Results: The optimal cutoff value of abnormal proteinuria and nephrotic range proteinuria was determined to be a protein–osmolality ratio (Up/Uosm) 0.27 and 1.59 mg/l/mOsm respectively. The correlation of 24-hr urinary protein excretion with both urinary protein/creatinine ratio (Up/Ucr) and Up/Uosm was highly significant (p<0.001). According to the receiver operator characteristic (ROC) curves analysis, we found no differences between Up/Uosm and Up/Ucr ratios in detecting either abnormal proteinuria or nephrotic syndrome. Conclusion: Urine protein to urine osmolality ratio seems to be a simple and a valuable test for the assessment of the degree of proteinuria in children.