We studied and quantified the healing process of gastric ulcers in humans by means of endoscopic ultrasonography. Initially, using the water bath method, we scanned specimens of resected human stomachs with gastric ulcers including 9 open ulcers and 14 ulcer scars. Comparison of histological findings and measurement of the cross-section suggested that the ulcers observed in the ultrasonographic photographs were essentially equivalent to those in histological photographs. By using endoscopic ultrasonography, we then examined 16 patients with active, mainly recurrent, gastric ulcers before and after 2, 4, and 8 weeks of H2 blocker treatment, measuring the length and cross-sectional area of the ulcer in endoscopic ultrasonographic photographs. From measurements of the contraction rate of cross-sectional ulcer area during healing, we observed that the healed ulcers showed a relatively rapid rate of contraction in the first 4 weeks of therapy and the non-healed cases showed a poor contraction rate. Endoscopic ultrasonography is useful for the quantitative estimation of histological changes associated with gastric ulcer healing.