Disturbances of hemostatic system may contribute to bleeding and thrombosis in patients with thalassemia. In this study, the plasma levels of natural anticoagulants and coagulant factors have been evaluated and the effect of chelation with desferrioxamine on those factors have been studied. The study group consisted of 20 children, aged 5-15 year, with beta thalassemia major. At the beginning of the study, 25% and 50% of children had decreased plasma levels of protein C and protein S, respectively. Following 1 year of chelation therapy, protein C and protein S levels did not change significantly. Antithrombin III levels were within the normal range both at the beginning and at the end of the study. Of the factors II, V, VII, VIII and IX, at the beginning of the study, 1 child had reduced factor II, another child had minimally reduced factor VII level and 2 children increased factor VIII and 1 child increased factor V levels. No correlation was noted between factor, protein C, protein S levels and ferritin and liver function tests. We conclude that children with thalassemia had decreased levels of protein C and protein S which are not associated with liver dysfunction and do not respond to chelation therapy with desferrioxamine. We also did not find significant alteration in levels of coagulation factors which may contribute to significant complication in hemostatic system.