BACKGROUND/AIMS Graft failure is a critical complication associated with vascular occlusion in esophageal reconstruction with a free jejunal graft following pharyngolaryngoesophagectomy. In this study, we evaluated the usefulness of intramucosal pH (pHi) measurement using a tonometer to assess the graft viability. METHODS Two consecutive studies, the early phase study and the late phase study, were performed. Nineteen patients who underwent free jejunal transfer were enrolled in the early phase study before 1999 to determine the critical pHi value. In the late phase study after 2000 (n=16), anticoagulant treatment to prevent graft necrosis was performed in the patients having a pHi value under the critical level. RESULTS In the early phase study, vascular obstruction was not seen in 16 patients with pHi>7.10. Of 3 patients with pHi<7.10, 2 underwent regrafting because of jejunal graft necrosis by vascular obstruction. In the late phase study, reoperation was not required in 3 of 4 patients with pHi<7.10. Intraoperative vascular occlusion was found in 1 patient with a decline in pHi value and anticoagulant treatment was effective in 2 others. CONCLUSION The pHi measurement using a tonometer is useful for finding vascular problems in free jejunal grafts.