Purpose: Renal size is an important indicator to determine adequate organ growth in children. The aim of this study is to estimate renal size with Tc-99m dimercaptosuccinic acid (DMSA) scan and propose a simple formula for predicting renal length in normal Korean children. Methods: This study included 346 children (198 boys and 148 girls, range 1 month-17 years) in whom renal length was measured with DMSA scan. Patients with anatomical renal abnormalities or acute pyelonephritis were excluded. Children were divided into two groups: 214 (61.8%) children were less than 1 year old (group 1) and 132 (38.2%) were 1 year of age or older (group 2). Results: Renal length was larger in left side than right side, and there was no significant difference of the renal length by gender. In 346 children, the formula for renal length was as follows: 4.682 x age (months) 0.137, R2=0.780. In group 1, the formula was renal length (cm) =0.127 × age (months) + 5.144, R2=0.354, and in group 2, 0.334 × age (years) + 6.477, R2=0.829. Conclusion: We proposed the formula to estimate renal length in Korean children over 1 year of age.