OBJECTIVE Jaundice is a common problem in neonatal period. Phototherapy is the most common treatment for neonatal jaundice. The purpose of this study was to determine the effect of adding white plastic cover around the phototherapy unit on hyperbilirubinemia in full term neonates with jaundice. METHODS In this randomized controlled trial, over 12 months (October 2009 - September 2010), 182 term neonates with uncomplicated jaundice, admitted to neonatal unit of Imam Reza Hospital (AS) in Kermanshah province of Iran, were selected. They were randomized in two groups. Control group received conventional phototherapy without cover around the apparatus and covered group received conventional phototherapy with plastic cover around the unit. After enrolment, total serum bilirubin was measured every 12 hours. Phototherapy was continued until the total serum bilirubin decreased to or less than 12.5 mg/dl. RESULTS There were no significant differences between the two groups for gestational age, birth weight, postnatal age, weight (at admission), serum level of hemoglobin, hematocrit and reticulocyte count. Total serum bilirubin in covered group, during the first 48 hours of treatment, declined significantly than in control group (P. value=0.003). The cover around the phototherapy unit not only did not increase the side effects of phototherapy, but also had a positive impact in reducing duration of jaundice (P. value <0.0001) and duration of hospitalization (P. value <0.0001). CONCLUSIONS The study results showed that using white plastic cover around the phototherapy unit can increase the therapeutic effect of phototherapy.