This case control study was conducted in Neonatal unit of Dhaka Shishu (Children) Hospital to assess the validity of fractional excretion of sodium (FENa) as a reliable renal function test in asphyxiated newborns. Seventy five appropriate newborns aged between 0-120 hours were randomized in two groups, (Group I; n=50, cases or study group) and (Group II; n=25, controlled group). Blood urea, serum creatinine, serum electrolytes, urinary electrolytes, creatinine, osmolalities, specific gravity, FENa were estimated. Blood urea, Serum creatinine and FENa are increased in perinatal asphyxia. Controls were selected from newborns who had spontaneous breathing immediately after birth and with Apgar score >8 to 10 at 5 minutes. Mean blood urea and serum creatinine were raised in asphyxiated newborn. Blood urea mean±SD was 7.1±3.1mmol/L and serum creatinine mean±SD was 120.8±73.6μmmol/L. Thirty four percent (34%) patients had raised level of blood urea and serum creatinine both, 18% patients had raised (>2.5%) FENa and 48% patients had raised blood urea in asphyxiated newborns. Hyponatremia was also found in asphyxiated newborns. Urinary sodium and creatinine excretion were also higher in the asphyxiated newborns than non asphyxiated newborns. Urinary volume and osmolality were similar in cases and controls. In this study 24% patients died, of which 62.5% were in HIE stage 3, 4.16% were in HIE stage 2 and 1% was in HIE stage 1. Elevated level of serum creatinine (130.0±60.0) and FENa (2.9±1.4) were found in dead patients. Oliguria (0.99±0.6) was also found in dead asphyxiated newborns. Increase in fractional excretion of sodium (FENa) is shown to be directly related to the degree of renal impairment which is again directly related to the degree of asphyxia in the newborns. FENa can be used as an indicator of renal tubular dysfunction in the asphyxiated newborns.