Abstract Background The Timed Up and Go (TUG) test is quick and easy tests to assess patients’ functional mobility. However, its reliability in individuals with knee osteoarthritis (OA) has not been well established. The aims of this study were to determine the reliability and minimal detectable change of the TUG test in individuals with doubtful to moderate (Grade 1–3) knee OA. Methods Sixty-five subjects (25 male, 40 female), aged 45–70 years, with knee OA participated. Inter-rater reliability was assessed using two observers at different times of the same day in an alternating order. Intra-rater reliability was assessed on two consecutive visits with a 2-day interval. The standard error of measurement (SEM) and the minimum detectable change (MDC) were calculated to determine statistically meaningful changes. Results Intra-rater and inter-rater reliability were 0.97 (95 % confidence interval [CI], 0.95 – 0.98) and 0.96 (95 % confidence interval [CI], 0.94 – 0.97), respectively. The MDC, based on measurements by a single rater and between raters, was 1.10 and 1.14 seconds, respectively. Conclusions The TUG is a reliable test with adequate MDC for clinical use in individuals with doubtful to moderate knee OA.