Objective Knee osteoarthritis is one of the most common musculoskeletal disorders affecting balance. It is also a risk factor for falling in older people. People with a history of falling, whether being injured or not, acquire a fear of potential falling, so they limit their functional activities, leading to decreased mobility, muscle weakness, and increased risk of falling in the future. Evaluating the relationship between balance and fear of falling in these patients can detect the disability mechanisms and falling and also help find more effective therapeutic methods for these patients. Some previous studies evaluated the stability of patients by clinical methods in static situations and related it to fear of falling. However, the walking stability of patients was not assessed by laboratory-based systems in previous studies. Therefore, we aimed to evaluate dynamic (during walking and based on the center of mass sways) and static stability (based on the center of pressure sways) and their relationship with falling risk in patients with knee osteoarthritis. Materials & Methods This is a descriptive cross-sectional study. A group of 15 subjects with mild to moderate knee osteoarthritis with a Mean±SD age of 50±3.22 years and 15 normal subjects with comparable age, height, and weight participated in this study. The subjects' standing stability was evaluated using a Kistler force plate based on mediolateral (ML) and anteroposterior (AP) displacements of the center of pressure. Also, the dynamic stability of the subjects was evaluated during walking and based on the center of massbase of support relationship in AP and ML directions. Kinematic data were collected using a motion analysis system with 7 high-speed cameras and a Kistler force plate. To model the body segments, the output of Qualisys track manager software was exported to Visual 3D software. Fear of falling was assessed by the native version of the fall efficacy scale (FES-I). The normal distribution of data was checked by the Shapiro-Wilk test. The independent samples t-test was used to compare the stability of patients and normal subjects. The Pearson correlation coefficient was used to evaluate the relationships between static and dynamic stability parameters and fear of falling in patients with knee osteoarthritis. Results Patients with knee osteoarthritis had less stability during standing and walking than healthy subjects (P<0.05). Moreover, based on the results of this study, there was a linear relationship between the center of body pressure (COP) excursions in the AP direction and the fear of falling scale. Still, it was not significant (r=0.416, P=0.123), and there was no correlation between the other COP parameters with FES (r=0, P>0.05). The correlations between mean center of mass (COM) excursion in AP and ML directions and FES were 0.309 and -0.123, respectively; however, these correlations were also not statistically significant (P>0.05). Conclusion Based on the results of this study, there is no significant relationship between static and dynamic stability of the patients with mild to moderate knee osteoarthritis (based on COP-COM variables) and the fall efficiency scale. So, it seems that to improve these patients' functional abilities, and the therapists must focus on the other parameters that affect the falling, such as reducing pain, improving proprioception, and enhancing muscle strength. It is suggested that future studies include a more varied age range of elderly people and evaluate all contributing factors in falling of patients with knee osteoarthritis (such as pain, proprioception, vision, and muscle strength) and also evaluate the stability of patients with both laboratory-based and clinical tests. [ABSTRACT FROM AUTHOR]