Background and Aim: This prospective observational study was designed aiming at evaluation of the possible effect of phototherapy on pro-oxidant/antioxidant balance (PAB) in newborns with jaundice. Patients and Methods: This study included forty newborns admitted to the NICU of Benha University Hospitals. The patients were full term, weighing > 2500 gm, aged between 2 and 14 days, with idiopathic unconjugated hyperbilirubinemia (bilirubin levels > 15 mg/dl) and were treated with phototherapy. All the studied patients were subjected to full medical history taking, complete clinical examination, and laboratory investigations as: complete blood count, ABO and Rh group, serum bilirubin total, direct and indirect, and PAB. Follow up investigations of serum total bilirubin (STB) levels, and PAB were recorded at the end of the phototherapy process. Results: The median pro-oxidant significantly increased after phototherapy (52.5 nmol/L) than before it (31.8 nmol/L) (P-value