Objective To investigate the anatomical and histological changes of the lengthened Rut by a special intraluminal tubular expander on the basis of the theory of ''tension-stress''. Methods Nineteen New Zealand white rabbits were used. A 5 cm segment of the terminal ileum with a pedicle was put underneath the abdominal wall, with its proximal end closed and its distal end exteriorized as a aroma. One week later, as the wound healed well, an expander made of a small rubber tube was inserted into the short gut loop through the stoma. Three milliliters of water was injected as an initial dose. Then 0.5 mi water as an increment was injected subsequently every 12 hours until the total amount of water reached 15 mi and kept stable for two weeks. Results Anatomically, the length and the capacity of the intestinal loop were recorded, alter 15 mi expanding, as an average of 150% lengthening of the original and an average of 293% expansion. Two weeks after the removal of the expander, partial shrinking was observed. A stable lengthening had 123% of the original length, while the capacity reduced to 200% of the original one. Histologically, there was no remarkable changes of the mucosa or submucosa. But significant hypertrophy of the musculature and serosa laver was observed. The total thickness of the musculatures was 618% of the normal control's. Ultrastructurally, there were enlargement of the smooth muscle cells, increase in number and size of the mitochondria in the cytoplasm and widening of the intercellular space. Conclusion A short gut can be lengthened by a tubular expander following the rule of gradual tension and stress.