Objectives and aim: Very low birth weight infants require 3 - 4 g/kg/day protein intake to provide satisfactory postnatal growth rates and neurodevelopmental outcomes. However, they have fewer functional nephrons, thereby increasing vulnerability for impaired renal functions. The aim of this study was to investigate the effect of different amounts of enteral protein intake during the fortification of human milk on renal glomerular and tubular functions. Material and methods: Preterm infants were randomized into three groups in terms of their daily protein intake: standard fortification (3 g/kg/d), moderate fortification (3.3 g/kg/d), and aggressive fortification (3.6 g/kg/d). Serum urea, creatinine (Cr), Cystatin C (Cys-C) and urinary 132 microglobulin (beta 2M) levels were assessed and compared between groups. Results: Serum urea, Cr, Cys-C and urinary beta 2M levels were similar in all three groups, both on discharge and postnatal Day 14 (p > 0.05). Mean Cr and beta 2M levels were significantly lower on discharge (p < 0.05), while Cys-C levels did not differ in time (p > 0.05). Conclusion: Enteral protein intake up to 3.6 g/kg/d did not alter the tubular and glomerular functions in very preterm infants. However, the long-term renal effects in these infants maintained on a high protein intake remain unknown and should be addressed in future studies.