BACKGROUND ABO-incompatible (ABOi) living donor liver transplantation (LDLT) was accepted as a feasible therapy for end-stage liver disease after the introduction of rituximab. The present study investigated the association between ABO incompatibility and graft regeneration in patients who underwent LDLT. MATERIAL AND METHODS A total of 335 adult patients who underwent elective LDLT were divided into ABO-compatible (ABOc) and ABOi LDLT groups using propensity score (PS) matching of graft regeneration-related factors. Postoperative serial changes in graft volumes were compared between the groups. The factors associated with graft volume on postoperative day (POD) 21 were investigated in patients who underwent ABOi LDLT. RESULTS In total, 300 (89.6%) patients underwent ABOc LDLT and 35 (10.4%) patients underwent ABOi LDLT. After PS matching, the ABOc and ABOi groups each included 32 paired patients. The absolute liver graft volumes on POD 21 were significantly lower in the ABOi group than those in the ABOc group in the PS-matched patients (1098.4 [964.0-1,162.0] vs. 1202.0 [1107.8-1455.2] mL; p=0.007). Major complications, including overall patient mortality during the follow-up period, did not differ between the groups. In patients who underwent ABOi LDLT, the preoperative graft volume/standard liver volume ratio and CD4+ cell level on POD 14 were independent factors related to liver graft volume on POD 21. CONCLUSIONS These results suggest that ABO incompatibility could affect postoperative liver graft regeneration. Therefore, graft regeneration must be investigated using a volumetric assessment in patients who have undergone ABOi LDLT.