Fifty two Wistar albino rats of both sexes were used for determination of the LD50 and some toxicological studies of the active principles of Euphorbia heliscopia (sun spourge). The oral LD50 was 1211.7 mg/kg. b.wt. of crude ethyl alcohol extracts under our environmental conditions. The symptoms appear on the intoxicated animals were included increase activity and irritability, salivation, itching the nose and mouth on the cage floor, and diarrhea. The animals were tried to make tunnels under the bed and they were reluctant to stand at the cage corners. Finally the animals closed its eyes and become calm. The animals administered high dose were died after a latent period (3 hours) and some of the animals in other groups were died within 24 hours. Concerning the haematological changes, there were no significant changes of PCV, Hb concentration, RBCs count, while there were significant increase of WBCs, and monocytes. Also there were highly significant increase and decrease of neutrophilis and lymphocytes respectively. The biochemical changes were reveled significant increase in creatinine, urea, uric acid, AST, ALP, cholesterol, T. protein and globulin. PM examination showed alveolar hemorrhages, proliferation of Kuppfer cells, necrosis infiltrated by lymphocytes in lung, liver and spleen. Hyaline deposits and pinkish staining proteineous deposits were seen in Bowman`s space of some glomeruli. It is concluded that E. heliscopia was a moderate toxic materials and must be avoided to introduce in the animal feed.