The purpose of this study is to define the effect of radiation hours on the physiologic jaundice infants. Since there in no full explanation of the way of phototherapy. Data was collected from February, 1993 through August, 1993 at E University Hospital. The subjects consisting of 179 normal newborn who is to receive phototherapy due to bilirubinemia in the early postnatal period. Six groups compared the effectiveness of phototherapy based on hours of radiation ; 6hrs, 9hrs, 12hrs, 15hrs, 18hrs, 21hrs. The results were as follows 1) Effectiveness of phototherapy which means serum total bilirubin decrements were significantly different in groups (F=9.812 p=.000). And follow up study was showed the subset in less than 15hrs groups and more than 15hrs groups. 2) There was no significant difference on the effect of phototherapy between aged after birth. 3) An hours of radiation and the number of stools was not revealed the relationship. The results obtained from this study suggest that 15hrs radiation per day is effective in phototherapy. In the furture, more replication of this study will be contribute for neonatal nursing care.