Abstract Introduction/Objective The Kidd blood group antigens are urea transporters found on the surface of red blood cells, renal tubular epithelial cells, and endothelial cells in the renal medulla and vasa recta. While controversial, some reports have described an association between Kidd antigen donor/recipient mismatches and kidney transplant rejection when recipients possess or form anti-Kidd alloantibodies. To date, none of these reports have described development of a thrombotic microangiopathy (TMA) in the renal graft associated with these antibodies. We describe a case of fulminant renal transplant rejection associated with TMA in a patient with anti-Jk(a) alloantibodies who received a deceased-donor kidney transplant (DDKT). Methods/Case Report A 64-year-old woman with end-stage renal disease secondary to AL amyloidosis caused by plasma cell neoplasm received a DDKT associated with delayed graft function. No pre- or post-transplant donor specific antibodies (DSA) were detected, the flow crossmatch testing was negative, and a pre-operative type and screen identified anti-Jk(a) alloantibodies. On post-transplant day 5, her creatinine remained elevated at 6 mg/dL (ref range: 0.4–1.3 mg/dL) with an acute drop in platelets and undetectable haptoglobin. Allograft biopsy showed a combination of TMA with some additional evidence of acute cellular rejection. Tacrolimus was stopped to rule out drug-induced TMA, and the workup showed negative Shiga toxin, normal ADAMTS13 activity, negative atypical HUS genetic testing, and negative antiphospholipid syndrome testing. Genotyping of the donor kidney was positive for the Jk(a) antigen. Eculizumab, IVIG, and a trial of 8 sessions of therapeutic plasma exchange (TPE) were administered. Her creatinine improved (1.93–2.05 mg/dL), indicating a significant antibody-mediated etiology to her delayed graft function. About one month later, her creatinine worsened, and she received another trial of TPE with IVIG and eculizumab. Despite a mild decrease in her creatinine, repeat biopsies showed acute cellular rejection, persistent TMA, and chronic allograft injury. No DSAs were ever detected. Her creatinine never recovered, and she is now dialysis-dependent. Results (if a Case Study enter NA) NA Conclusion We speculate that anti-Jk(a) antibodies interacting with a Jk(a)-positive donor kidney account for graft TMA. This case underscores the potential importance of matching Kidd antigens in kidney transplantation.