The study showed a significant difference in CD19+ lymphocytes percentage between patients before phototherapy and controls (P value<0.01), also a significant correlation between serum levels of total bilirubin in patients and CD19+ lymphocytes percentage (P value<0.05). There was no significant difference between the percentages of CD19+, CD4+ and CD8+ lymphocytes in patients before or after 72h of exposure to phototherapy (P value>0.05). Also, there was no correlation between the percentages of CD19+, CD4+ and CD8+ lymphocytes after 72h of exposure to phototherapy and the occurrence of infections (Gastrointestinal tract and Respiratory tract infection) after six months of follow-up (P value>0.05). More studies are needed with larger number of patients to determine the effect of phototherapy on immune system.