For the purpose of studying digestion and absorption disorders following stomach surgery, particularly with respect to membrane digestive functional disorders, morphological and enzyme-histochemical observation of the small intestinal mucosa was performed, and a comparison was done between the partial gastrectomy group (59 cases), and the total gastrectomy group (52 cases). The following results were obtained: 1) The small intestinal mucosa showed a tendency to significant villous atrophy in post-operative groups. 2) There was a significant decrease in the disaccharidase activity, especially in the small intestine of the total gastrectomy group. ALP, LAP and gamma-GPT activity also decreased, or disappeared in the small intestines showing villous atrophy. 3) In the atrophied mucosa which showed a marked decrease in membraneous enzyme activity, poorly-formed, irregularly sized microvilli accompanied by glycocalyx irregularity and disappearance were recognized under the electron microscope. The above mentioned morphological and enzyme-histological findings in the small intestinal mucosa, were strongly reflected in both post-operative progress and clinical symptoms.