Abstract： Background::Synovectomy has been introduced into total knee arthroplasty (TKA) with the aim of relieving pain and inflammation of the synovium. However, there are no long-term, comparative data to evaluate the effect of synovectomy in TKA. This study was aimed at assessing pain, function, and complications in patients undergoing synovectomy during TKA for osteoarthritis (OA) at long-term follow-up.Methods::This was a prospective randomized controlled trial of 42 consecutive patients who underwent staged bilateral TKA. Patients undergoing the first-side TKA were allocated to receive TKA with or without synovectomy followed by a 3-month washout period and crossover to the other strategy for the opposite-side TKA. The overall efficacy of both strategies was evaluated by determination of blood loss, the Knee Society score (KSS), and knee inflammation conditions during a 3-month postoperative period. The postoperative pain, range of motion (ROM), and complications were sequentially evaluated to compare the two groups until 10 years after surgery.Results::At the 10-year follow-up, both groups had a similarly significantly improved ROM (114.88 ± 9.84° vs. 114.02 ± 9.43°, t = 0.221, P = 0.815) and pain relief with no differences between the two groups (1.0 [1.0] vs. 1.0 [1.5], U = 789.500, P = 0.613). Similar changes in total blood loss, KSS, and knee inflammation were found in both groups during 3 months postoperatively ( P > 0.05). Additionally, there was no significant difference regarding complications and satisfaction between the two groups ( P > 0.05). Conclusions::Synovectomy in conjunction with TKA for primary OA does not seem to provide any benefit regarding postoperative pain, ROM, and satisfaction during a 10-year follow-up. In addition, it may not result in more blood loss and increased incidence of long-term complications. Based on our long-term findings, it should not be performed routinely.Trial registration::Chinese Clinical Trial Registry, ChiCTR-INR-16008245; https://www.chictr.org.cn/showproj.aspx?proj= 13334.