Simple,functional tests like Timed Up and Go test (TUG),5 Times Sit to Stand test (STS) and 10 meters Walk test (WT) completed with measurement of strength of knee extensors and flexors are often used in clinical trials. 61 patients with symptomatic knee OA were included in this study. Testing protocol consisted of TUG,STS,10WT and Maximal Voluntary Isometric Contraction(MVIC) of knee extensors and flexors.Participants were tested twice with this protocol.Patient rested in a comfortable position for about 30 minutes and then proceeded with a second trial. Functional tests:TUG,STS and 10WT showed an excellent test-retest reliability.ICC(2.1) were 0.951,0.955 and 0.974, respectively.MVIC and MVICstandarised of knee extensors and flexors showed an excellent test- retest reliability. ICC(2.1) were 0.968 and 0.969 for MVIC of extensors and flexors, respectively.For MVICstandarised of extensors and flexors ICC(2.1) were 0.968 and 0.969,respectively. SEM and MDC95 for TUG was 0.37s and 1.01s,respectively; for STS was 0.69s and 1.91s,respectively; for 10WT was 0.23s and 0.65s,respectively; for MVIC of extensors was 19.66N and 54.5N,respectively; for MVIC of flexors was 9.73N and 26.96N,respectively; for MVICstandarised of extensors was 0.22 and 0.62,respectively; for MVICstandarised of flexors was 0.11and 0.31,respectively. TUG, STS, 10WT and MVIC measurement of knee extensors and flexors have an excellent test- retest reliability in patients with mild to moderate knee OA. Changes greater than 1.01s for TUG, 1.91s for STS, 0.65 for 10WT, 0.62 for MVICstandarised of knee extensors and 0.31 for MVICstandarised of knee flexors may be used as a clinically significant.