Abstract: Human coagulation factor V serves as a cofactor for factor X in thrombin formation. Generation of thrombin leads to fibrin and clot formation. In this study 65 patients were selected with venous thrombosis. Patients with a positive Protein C resistance were chosen and screened genetically by Conformation Sensitive Gel Electrophoresis (CSGE) for the presence of factor V mutations, the suspected mutations were sequenced. Three new mutations were found as follows, Met 385 thr, Met 1736 Val and Lys 386 Lys. Present study shows factor V mutations leading to thrombosis that have been never reported in Iran