Introduction: The 6-Minute Walk Test (6-MWT) is a simple and commonly used functional performance test that assesses an individual's aerobic capacity and endurance of the lower limb. In knee osteoarthritis, the 6-MWT is often employed as a clinical assessment tool to evaluate functional capacity and monitor changes in physical performance over time. Individuals with knee osteoarthritis may experience pain, stiffness, and reduced mobility, significantly impacting their ability to walk and engage in daily activities.  Aim: This study determines the reliability, construct validity, and minimal detectable change of 6-MWT in patients with knee OA.    Materials and Method: This was an Observational Cross-sectional study. This study was conducted at The Sarvajanik College of Physiotherapy, Surat for a period of one year i.e. from July 2022 to June 2023. A total of 90 patients with knee OA were selected as participants, and the study used outcome measures such as mWOMAC to assess the level of disability and 30s SST to examine the Functional capacity and Strength of the lower limbs. Only 44 of 90 participants performed 6-MWT again after 48 hours for reliability. Data obtained were analysed in SPSS version 20.0. Intra-class correlation coefficient (ICC) values were derived for test-retest reliability, Pearson's correlation was seen for validity assessment, and standard error of measurement (SEM) and minimum detectable change (MDC) were also calculated.  Results: The mean age of the patient was 59.66±8.237, and the mean pain score was 6.04±1.805. The ICC values for test-retest reliability were 0.992, which showed excellent reliability. The SEM and MDC values were 9.018 meters and 24.92 meters, respectively. 6-MWT showed a high-level positive correlation with the 30sSST (r = 0.821) and a moderate negative correlation with the mWOMAC and NPRS (r = -0.593 & r = -0.537), respectively.  Conclusion: The 6-minute walk test is a reliable, valid test to assess the functional capacity in knee OA patients.