Abstract: Objective To evaluate perioperative occult blood loss following total knee arthroplasty(TKA).Methods A retrospective analysis of 40 patients undergoing TKA was conducted to calculate the mean blood loss and occult blood loss according to Gross formula.Results The mean total blood loss was 1538 ml in these cases with occult blood loss of 791 ml.In patients with autologous blood transfusion,the mean total blood loss was 1650 ml with occult blood loss of 786 ml.In patients without autologous blood transfusion,the mean total blood loss was 1370 ml with occult loss of 798 ml.Conclusion TKA often results in large volume of occult blood loss in the perioperative period which can not be fully compensated by autologous blood transfusion,and additional blood supply is needed for maintenance of the circulating volume.