Unicompartmental knee arthroplasty (UKA) is one of the effective surgical methods for the treatment of unicompartmental knee arthritis. When UKA fails, a revised surgery to total knee arthroplasty (TKA) is often necessary. The purpose of this study was to compare the clinical outcomes of revision of failed UKAs to TKAs with primary TKAs. The hypothesis was that the TKAs revised from UKAs had inferior clinical outcomes compared with primary TKAs. This meta-analysis was conducted in accordance with the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines. Newcastle-Ottawa Scale (NOS) proposed by the Cochrane Collaboration was used for evaluating the methodological quality of the studies. PubMed, Medline, Embase, Web of Science, and the Cochrane Library were searched to identify studies that compared the revision of UKA to TKA with primary TKA. Primary outcomes included Range of motion (ROM); Knee society score (KSS); (re-)revision rate and complications. Secondary outcomes were blood loss and length of hospital stay. A total of 8 eligible retrospective comparative studies were identified from a keyword search. Results revealed that the primary TKAs group has a better ROM (MD=-7.29, 95% CI: -14.03-0.56, P<.05), higher Knee Society Knee scores (MD=-0.54, 95% CI: -1.12-0.04, P<.05), higher Knee Society function score (MD=-0.65,95% CI: -1.25-0.06, P<.05), lower (re-) revision rate (MD=4.15, 95% CI: 2.37-7.25, P<.05) than rUKAs. There was no significant difference in postoperative complications, blood loss and length of stay between the 2 groups. Our meta-analysis revealed that compared with primary TKAs, TKAs revised from UKAs had inferior clinical outcomes.