Objective To explore the effect of prenatal steroid (PNS) treatment on preventing early severe non-oliguric hyperkalemia in Extremely-Low-Birth-Weight (ELBW) infants.Methods Retrospective comparative analysis was performed on 31 ELBW infants who had been admitted to the hospital’s NICU between July 2001 and Jun 2005. Infants whose mothers received a full course of steroids before delivery (PNS group; n=18) were compared with those infants whose mothers did not receive steroids (NSG group; n=13). Infants were included in the PNS group if their mother was given one full course of dexamethasone ( 10 mg q12h4 doses) before delivery. The last dose must have been given at least 24 hours before delivery. The arterial blood gas , serum concentrations of potassium, sodium and creatinine were measured every 24 hours, and fluid intakes, urine outputs were monitored every day. Results Hyperkalemia was significantly lower in the PNS than in the NSG infants at the first 72 hours of age [5/18 cases ( 27.78%) vs 9/13 cases (69.23%)],P=0.023). However, the serum concentrations of sodium, creatinine, fluid intakes, urine outputs were not significantly difference in both groups. Conclusions Prenatal steroids treatment can reduce early severe non-oliguric hyperkalemia in EVBL infants.