Background:Postoperative care has been evolving since the concept of enhanced recovery after surgery (ERAS) was introduced in China.This study aimed to evaluate the effects of early ambulation within 24h after unilateral total knee arthroplasty (TKA) on postoperative rehabilitation and costs in a Chinese population.Methods:This cohort study of patients with knee osteoarthritis who had undergone TKA at 24 large teaching hospitals between January 2014 and November 2016 involved 2687 patients who began ambulating within 24h (Group A) and 3761 patients who began ambulating later than 24h (Group B).The outcome measurements,such as length of stay (LOS),total hospitalization costs,dynamic pain level,knee flexion range of motion (ROM),results of the 12-Item Short Form Survey (SF-12),incidence of thromboembolic events and other complications,were recorded and compared.Results:The early ambulation group (Group A) had a shorter LOS and lower hospitalization costs and pain levels than the late ambulation group (Group B).There was a favorable effect in enhancing ROM for patients in Group A compared with patients in Group B.In Group A,patients had significantly higher postoperative SF-12 scores than those in Group B.The incidence of deep venous thrombosis (DVT) and pulmonary infection was significantly lower in Group A than in Group B.The incidence of pulmonary embolism (PE) and other complications did not differ between the two groups.Conclusions:Early ambulation within 24h after TKA was associated with reduced LOS,improved knee function,lower hospitalization costs and lower incidence of DVT and pulmonary infection in the Chinese population.