This study was conducted to determine the neutrophil/lymphocyte ratio, lymphocyte/monocyte ratio, platelet/lymphocyte ratio; and to evaluate the effect of phototherapy on the peripheral blood cells in newborns with indirect hyperbilirubinemia. A total of 180 newborns consisting of 119 hyperbilirubinemic newborns, who received phototherapy; and 61 healthy newborns were included in the study. A statistically significant difference was present only between the patient group and healthy newborn white blood cell values after phototherapy. The differences found for pre-phototherapy neutrophil/lymphocyte ratio and lymphocyte/monocyte ratio values were statistically significant, but no statistical significance was present for the values after phototherapy. These results suggest that phototherapy may have an effect on peripheral blood cells by directly decreasing both the cytokine and bilirubin levels. The decrease in neutrophil/lymphocyte ratio and lymphocyte/monocyte ratio after phototherapy could potentially be used in the evaluation of phototherapy's effect on peripheral blood cells. New studies on this subject are, therefore, required. Key Words: Newborn, Phototherapy, Inflammation, Peripheral blood cells.