We report a 48-year-old man presenting with refractory hyperammonemia after orthotopic liver transplantation. On investigation he was found to have acquired hepatic glutamine synthetase deficiency, a rare condition that occurs after organ transplantations. The patient was started on continuous venovenous hemofiltration treatment, but the hyperammonemia did not respond. The patient was then subjected to molecular adsorption recirculation system (MARS) therapy and the ammonia level gradually improved with successive treatments. In conclusion, the response was unlikely due to the hemofiltration component of MARS alone but more probably due to the removal of putative albumin-bound toxin by the adsorption circuit that had ameliorated the internal milieu of the graft and reversed the enzyme deficiency.