Objective To evaluate the effects of ABO blood group factors on perioperative coagulation in patients following epidural anesthesia.Methods One hundred and twenty ASA I or Ⅱ patients,aged 30-50 yr,weighing 50-75 kg,scheduled for elective operations expected to cause small volume of blood loss during operation under epidural anesthesia,were divided into 4 groups according to the blood group (n =30 each):blood group A group (A group),blood group B group (B group),blood group AB group (AB group) and blood group O group (O group).Blood samples were taken from the central vein before anesthesia (baseline,T1),at 30 min after beginning of operation (T2),at the end of operation (T3),and at 1,8 and 24 h after operation (T4-6) for determination of prothrombin time (PT),activated partial thromboplastin time (APTT),fibrinogen (Fib) concentration,thrombin time (TT),prothrombin activity (PTA),hematocrit (Hct),and platelet (Plt) count.Results The parameters of coagulation were within the normal range at T1-6 in each group.Compared with the baseline value at T1,Fib concentration was significantly decreased,and PT,TT and APTT were increased at T2-6 in O group (P ＜0.05),however,no significant change in all parameters was found at T2-6 in the other three groups (P ＞ 0.05).Fib concentration was significantly lower,and PT,APTT and TT were longer at T1-6 in O group than in A,B and AB groups (P ＜ 0.05 or 0.01).Conclusion Although perioperative coagulation is in the normal range under epidural anesthesia in patients of different ABO blood groups,the coagulation is decreased in patients of blood group O as compared with the other blood groups.