Aim To determine the effectiveness of a self‐management support intervention on knee functional status and health‐related quality of life among middle‐age women with knee osteoarthritis. Design Randomized controlled trial. Methods The participants were 40 middle‐aged women who had been clinically diagnosed with knee osteoarthritis for more than 3 months and randomly assigned into intervention and control groups equally. After IRB approval code 02‐05‐2562 was obtained, data collection was carried out from July – November 2019 at the Outpatient Department of Orthorpedics, Thasala Hospital, Thailand. The modified Thai version of the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) and the Short Form Survey (SF‐36) were used to measure knee functional status and health‐related quality of life at baseline (T1), immediately after completing the intervention (T2) and 4 weeks after the intervention (T3). The participants in the intervention group received a self‐management support program developed by the researcher based on the Individual and Family Self‐Management Theory and a review of related literature plus routine care. The implementation consisted of eight sessions over 4 weeks. The control group received only routine care from the hospital. Two‐way repeated measure ANOVAs were used to analyze the data. Results The findings revealed that the participants in the intervention group had better knee functional status and HRQOL than those in the control group at follow‐up. Additionally, in the intervention group, both knee functional status and HRQOL significantly improved from pre‐ to post‐intervention and follow‐up. Conclusions The findings indicate that this self‐management support intervention is effective. Impact For women, the prevalence rate of knee OA rises dramatically post‐menopause due to lower oestrogen levels. Policy makers and healthcare providers could obtain and promote this intervention as part of standard practice. This should lead to improved knee functional status and HRQOL among middle‐aged women. Thai Trial Registration number: TCTR20191223003. on February 5th, 2019