The aim of this research is to determine the characteristics of endothelial factors and the hemostatic system conditions with malignant neoplasms patients, which were exposed to ionizing radiation. Total number of examined people is 223, 153 of them are patients with gastrointestinal tract oncopathology. The article presents the results of the analysis of numerical indicators of endothelial condition and platelet hemostasis of patients, who had cancer. They lived in the regions of Kazakhstan, subjected to contamination of radionuclides as a result of nuclear weapons tests, which took place in this region from 1949 to 1989. These results then were compared to cancer patients and healthy individuals with no radiation risk. The study revealed the presence of higher levels of endothelial dysfunction and following trigger of the hemostatic system in patients with malignant tumors of the gastrointestinal tract. In particular, the defined high degree of endothelial dysfunction include endotheliumdependent vasodilation, content desquamated endothelial cells in peripheral blood and von Willebrand factor. These indicators have a clear correlation with the degree of disorder of studied parameters of the hemostasis, which can cause the development of thrombotic complications.