Introduction: While the routine administration of Rhesus immunoglobulin has significantly reduced the incidence of this type of alloimmunization, maternal alloimmunization to other red cell antigens continues to contribute to perinatal morbidity and mortality. Although the Kell antigen is found on the red cells of only 9% of the population, attention has increasingly been focused on Kell antibodies. Case Report: We present a case of fetal hydrops who was sonographically detected at 30th week of pregnancy. Antenatal tests for evaluation of fetal condition clearly showed the critical level of hemolytic disease but the baby was delivered prematurely due to fetal distress. The combination of anemia, reticulocytopenia, hydrops fetalis, and positive indirect Coombs test suggested Kell isoimmunization. The baby was treated by exchange transfusion with the Kell-negative packed red cell succesfully, and was discharged on postnatal 30th day. Conclusion: Here we describe a case of hydrops fetalis caused by Kell alloimmunization that was determined in postnatal period, and thus we plan to discuss the perinatal approach to the Kell immunization.