For the diagnosis of hemolytic disease of newborn especially due to ABO group incompatibility, presence of immune antibody in blood of mother and/or infant is essential. Rosner's modified 2-Mercaptoethanol reduction method is simple and sensitive. With this method we have conducted some basic stuffy of immune antibody in multiparous women with blood group 0 and The results are as fellows; 1) The mean immune antibody titer of group 0 multiparous women (1:8) is significantly higher than control group (1:2) who are group 0 girls without history of transfusion or pregnancy. 2) Mean immune antibody titer is significantly different according to their husband blood groups. Group 0-A couple has higher antibody titer (1:16) than group 0-B or group 0-0 couple 3) Immune antibody titer shorts no significant correlation with age, number of pregnancy or time lapse from last delivery. In conclusion a newborn who is born to group 0 mother and group A father is most subject to ABO hemolytic disease of newborn than other blood group combinations. Antenatal determination of immune antibody titer in group 0 mother could be helpful for the diagnosis and prediction of development of ABO hemolytic disease of newborn.