Although thoracoscopic lobectomy in a lung cancer patient with hemophilia is already reported but this is the first report of a VATS lobectomy in a patient with FXI deficiency. Inherited factor XI (FXI) deficiency is a rare autosomal coagulation disorder with an estimated prevalence of 1 in 1,000,000 individuals. Since FXI is part of the intrinsic coagulation system, FXI-deficient patients have a prolonged APTT but a normal-range PT. If an especially prolonged APTT is obtained, FXI activity should be measured along with other coagulation factors. Although the bleeding diathesis in FXI-deficient patients is considerably milder than that in hemophilia A or B, bleeding is nonetheless observed in 9.6% of such patients in the context of surgical procedures including tooth extractions, tonsillectomies, and nasal operations. It has been reported that it may be difficult to distinguish severe and mild deficiency on clinical grounds alone, and the lack of a method to reliably distinguish FXI-deficient patients who may bleed from those without such a predisposition has been noted. Given the invasiveness of the procedure in our case, it was thought that replenishment of coagulation factors prior to surgery was needed to avoid life-threatening bleeding. Because human plasma-derived FXI concentrates, which have been shown effective in replenishing XI factor, are not available in Japan, replenishment therapy here is done by FFP transfusion. The main disadvantages of this therapy are the potentials for transmission of infection agents, allergic reactions and volume overload. It is important to confirm preoperative cardiac function to avoid acute heart failure due to volume overload by transfusion.