OBJECTIVE: To explore special coagulation characteristics and anticoagulation management in extracorporeal membrane oxygenation (ECMO)-assisted patients with coronavirus disease 2019 (COVID-19). DESIGN: Single-center, retrospective observation of a series of patients. PARTICIPANTS: Laboratory-confirmed severe COVID-19 patients who received venovenous ECMO support from January 20-May 20, 2020. INTERVENTIONS: This study analyzed the anticoagulation management and monitoring strategies, bleeding complications, and thrombotic events during ECMO support. MEASUREMENTS AND MAIN RESULTS: Eight of 667 confirmed COVID-19 patients received venovenous ECMO and had an elevated D-dimer level before and during ECMO support. An ECMO circuit pack (oxygenator and tubing) was replaced a total of 13 times in all 8 patients, and coagulation-related complications included oxygenator thrombosis (7/8), tracheal hemorrhage (5/8), oronasal hemorrhage (3/8), thoracic hemorrhage (3/8), bleeding at puncture sites (4/8), and cannulation site hemorrhage (2/8). CONCLUSIONS: Hypercoagulability and secondary hyperfibrinolysis during ECMO support in COVID-19 patients are common and possibly increase the propensity for thrombotic events and failure of the oxygenator. Currently, there is not enough evidence to support a more aggressive anticoagulation strategy.