Abstract: Sheep were infected experimentally with Theileria uilenbergi by subcutaneous injection, and the pathology of theileriosis was observed. The results showed that the principal microscopic founding was hyperaemia, hemorrhage and proliferation of reticuloendothelial cell in lymph nodes, proliferation of interstitial lymphocytes and reticular cells in lung, and thickened alveolar septum, proliferation of glomerular endothelial cells and vascular endothelial cells in kidney. Lymph reticulocytes were accumulated into a tubercle in kidney. Cardiac muscle cells showed apomorphosis and uneven dyeing. The tunica propria was obvious hyperaemia and hemorrhage in the intestinal tract. Additionally, the hepatocytes showed granular degeneration and necrosis. Various degrees of haemorrhage were seen in submucosa and muscle layer of rumen.