Objectives: The aim of this study was to examine the relationship between the body composition measures and knee osteoarthritis (OA) inpostmenopausal women to determine whether the fat mass or the lean mass was closely associated with knee OA.Patients and methods: This retrospective, cross-sectional study included a total of 212 postmenopausal women (mean age 59.9±6.2 years;range, 46 to 76 years). Descriptive characteristics were recorded and height was measured using a stadiometer. Body weight, fat mass, andlean mass were estimated using bioelectrical impedance analysis. X-rays of the knees were obtained. Knee OA was radiographically diagnosedaccording to the Kellgren-Lawrence criteria. Based on the radiographic knee OA diagnosis the women were divided into two groups. Logisticregression analyses were used to examine the associations between the body composition measures and knee OA.Results: Knee OA was present in 117 women. Body Mass Index, body weight, fat mass, and lean mass were all significantly associated withknee OA after adjusting for confounding factors such as age, height, and physical activity (p<0.001). When assessed together with leanmass in a multivariate regression model, fat mass was closely and significantly found to be related to knee OA, compared to lean mass(p<0.001, OR: 1.17). Furthermore the fat mass/lean mass ratio was positively associated with knee OA (p<0.001).Conclusion: In postmenopausal women body weight was significantly and positively associated with knee OA and among the componentsthat constitute body weight, fat mass was closely and significantly associated with knee OA compared to lean mass. This result suggests thatthe relationship between obesity and knee OA is mainly based on the fat mass, and supports the importance of systemic metabolic effects ofadiposity in this relationship.