In order to study the immunohistochemical effects of Opae-san on gastric ulcer induced by HCl-aspirin in rats, experiments were done by oral administration and measure histological features of ulcer lesion, scaning electron microscopic appearance, the changes of numbers of parietal cells, chief cells, gastrin and somatostatin-immunoreactive cells. The obtained results are as follows: 1. Ulcerative lesions were numerously detected in control groups especially in junction of cardiac-fundic gastric mucosa and histologically very severe injury to gastric epithelium were observed too but in the Opae-san administrated groups, no gross lesion of ulcer were detected and histologically minor injury of gastric mucosa were observed. Most slight injuries to gastric mucosa were observed in 5 days after treatment. 2. The numbers of parietal cells were remarkably increased in control group but in Opae-san administrated groups appeared significant decrease compared to control groups. Most remarkably decrease of the numbers of parietal cells compared to control groups were observed in 5 days after treatment. 3. The numbers of chief cells were remarkably decreased in control group but in Opae-san administrated groups appeared significant increase compared to control groups. Most remarkably increase of the numbers of chief cells compared to control groups were observed in 5 days after treatment. 4. The numbers of gastrin-immunoreactive cells were remarkably decreased in control group but in Opae-san administrated groups appeared significant increase compared to control groups. Most remarkably decrease of the numbers of gastrin-immunoreactive cells compared to control groups were observed in 5 days after treatment. 5. The numbers of somatostatin-immunoreactive cells were remarkably decreased in control group but in Opae-san administrated groups appeared significant increase compared to control groups. Most remarkably decrease of the numbers of somatostatin-immunoreactive cells compared to control groups were observed in 5 days after treatment. 6. Scaning electron microscopically, severe denude and degeneration of gastric mucosa were observed in control groups but in Opae-san administrated groups the lesions were remarkably decreased compared to control groups.