ABO HEMOLYTIC disease of the newborn is the most common cause of HEMOLYTIC jaundice in newborns. In a prospective study during] 997, we determined the clinical course and incidence of HEMOLYTIC disease of newborn due to ABO blood group incompatibility in Ghaem Hospital.In the present study from a sample of 128 blood group (O) mothers, 50 term neonate, had blood group A & B as case group, and 50 neonates without incompatibility considered as control group these infants were compared for hyperbilirubinemia in first 3 days of life.Skin Bilirubin index, measured daily in both groups of newborns byjaundicemeter instrument. In babies with critical index (skin Bilirubin> 17) serum bilirubin and other Hematological values were determined.In this study, six newborns had significant jaundice (Bilirubin>15mg/dl) in incompatible group but in control group only 2 infant had hyperbilirubinemia in first three day of life.Taking into account that in Mashhad their frequency & blood 0 is nearly 60%, it was concluded that in general population of pregnant mothers 24%, Present feto- maternal ABO incompatibility.This figure is less than value that reported by others, therefore, incidence of ABO- HEMOLYTIC disease in all of newborns is 2/9 percent (%24).