Rationale: Graft-derived-cell-free DNA (Gcf-DNA) in plasma was a promising biomarker to monitor graft-rejection transplantation. However, little is known about the application of Gcf-DNA in living-donor-liver-transplantation (LDLT). Patients concern: In this study. 2 patients diagnosed with Ornithine Transcarbamylase Deficiency (OTCD) were enrolled and indicated for LDLT. Diagnoses: Two patients were genetically diagnosed with OTCD, and they suffered from recurrent and uncontrollable hyper-ammonemia and failed in accepting the normalized OTCD treatments, such as decreasing dietary nitrogen intake and increasing waste-nitrogen excretion. Interventions: LDLT was performed in the 2 patients uneventfully, and we collected circulating cell-free DNA from plasma in specific postoperative time points (day 1, day 7, day 14, day 30, day 60). Since both of the recipients were sex-mismatch with the donors, we measured Gcf-DNA through the Y-chromosome method and compared it with the routine liver function. Outcomes: The result showed that Gcf-DNA had the similar discrimination of graft injury trend while compared to routine liver function. The follow-up showed these 2 patients' status is stable. Lessons: Applying Gcf-DNA to monitor graft injury in LDLT is promising, but still long term follow-up and more samples are needed for validation.