Coagulation disorders and abnormal platelet activation are frequent findings in hematological malignancies. A hypercoagulable state is induced by malignant cells interacting directly with haemostatic system and activating the coagulation cascade. This is descriptive, prospective analytical case- control study done in Radiation & Isotopes Center Khartoum (RICK) to determine the haemostatic abnormalities and vascular damage of hematological malignancies among the major Sudanese patients.Hemostasis studies shown that, there were decreased level of fibrinogenand antithrombin III, vWf and PAI-1 were significantly elevated in ALL and in AML patients. significantly low platelet counts in AML, CLL and increased in CML and CGL ( CML ph positive) in related to control group. D-dimers was positive in 79 % of patients.platelet aggregation in response to ADP, Collagen, and Epinephrine agonists was decreased in ALL, AML and MM, and in variable in CML and NHL, and increased in CLL and HL.Markers of coagulation and platelet defect was clearly observed in hematological malignancies patients, also indication of fibrinolysis and endothelial activation were confirmed