To evaluate the effects of conventional phototherapy and fiberoptic phototherapy on trans-epidermal water loss in preterm infants with and without skin ointment application, 20 infants were randomly assigned to receive conventional or fiberoptic phototherapy for non-hemolytic hyperbilirubinemia. After conventional phototherapy, there were no significant differences in trans-epidermal water loss between ointment-treated and untreated areas. After fiberoptic phototherapy, trans-epidermal water loss significantly increased from ointment-treated and untreated areas, but the increase was less in treated areas.