Summary Background: Hypomagnesaemia is a frequent complication after liver transplantation (LTx) however; magnesium is not routinely replaced in the perioperative period. Material/Methods: The incidence of hypomagnesaemia before and after pediatric LTx was studied in 673 pediatric patients who underwent living-donor liver transplantation (LDLT). Results: The mean serum Mg levels before LTx was normal, 2.03±0.28 mg/dl, exhibited marked decrease on 5th postoperative (PO) day, 1.79±0.45, p0.001, comparing with the pretransplant value. It reached its nadir in the 1st PO month, p0.001. Up to the 5th PO year, serum Mg did not achieve the lower limit of normal, 1.77±0.24, p0.001 and incidence of hypomagnesaemia was 60.7% (242/399). Univariate analyses of variables that can predict graft loss and patient death after LDLT demonstrated that recipient factors, pre and post transplant serum Mg and blood product transfusions were potentially risk factors significantly affected the outcome. Multivariate analysis of potential risk factors showed that pre transplant serum Mg 1.8 mg/dl, (Hazard ratio (HR) 2.362 [confidence interval (CI) 1.350–4.133]; p=0.003) and pre transplant BUN, (HR 1.046 [CI 1.014–1.079]; p=0.005) were independent predictors of graft loss and patient death. Conclusions: hypomagnesaemia is common before and after pediatric LDLT. Pre transplant hypomagnesaemia and high BUN are independent risk factors for graft loss or patient death. Pre transplant hypomagnesaemia patients exhibited decreased survival of their graft. Post transplant hypomagnesaemia was a potentially risk factor for graft loss.