The experimental study was performed to evaluate the microvascular changes in postirradiation injury of small intestine. With a total of 28 rats, 24 rats were on right upper quadrant of abdomen with a single dose of 2000 rads and each group of 4 rats were followed up in 1,2,4,5,12 and 16 weeks and remaining 4 rats were used for normal control group. Evaluation of the microvascular changes were done by observing both mocroangiographic and histopathologic findings in groups of each follow-up week. The results were as follows: 1. The main microangiographic findings were strethcing and diffuse narrowing of vessels and extravasation of microbarium in post-irradiation 1-4 weeks, and focal narrowing and dilatation, irregular branching pattern and tortuosity of vessels in post-irradiation 8-16 weeks. Poor opacification of capillary network was continuously observed in all follow-up period. 2. The degree of vascular tortuosity in microangiography was consistent with the degree of vascular wall thickening in histopathollgy. 3. It is inferred that the results in this experimental study with microangiography can be used as a guide line for further studies of post-irradiation injury of small intestine.