A Jr(a-) female (proposita) who has developed anti-Jra during her second pregnancy and her pedigree chart are reported. The antibody anti-Jra of the proposita and her baby was determined to be IgG and was eluted from their red cells. The baby's bilirubin rose to a peak on day 4 without clinical problem except for prophylactic phototherapy carried out. Two other examples of Jr(a-) blood type were detected in her elder sister and the first baby of the proposita with investigation of her pedigree chart.