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The objectives of this cross-sectional study were to examine whether older Tai Chi practitioners had better knee muscle strength, less body sway in perturbed single-leg stance, and greater balance confidence than healthy older adults.Tai Chi and control subjects (N = 24 each, aged 69.3 ± 5.0 and 71.6 ± 6.1 yr, respectively) were matched with respect to age, gender, height, weight, and physical activity level. Concentric and eccentric isokinetic tests of the subjects” dominant knee extensors and flexors were conducted at an angular velocity of 30°·s−1. Control of body sway was assessed in static double-leg stance and in single-leg stance perturbed by forward or backward platform perturbations. The Activities-specific Balance Confidence (ABC) scale was used to investigate subjects” balance confidence in daily activities.Tai Chi practitioners had higher peak torque-to-body weight ratios in concentric and eccentric isokinetic contractions of their knee extensors and flexors (P = 0.044). They manifested less anteroposterior body sway angles in perturbed single-leg but not static double-leg stance than did control subjects (P < 0.001). Tai Chi practitioners also reported significantly higher balance confidence score ratios (P = 0.001). Older adults” knee muscle strengths showed negative correlations with body sway angles in perturbed single-leg stance and positive correlations with ABC score ratios. Moreover, their body sway angles in perturbed single-leg stance were negatively correlated with their ABC score ratios (all P < 0.05).Our results demonstrate that long-term Tai Chi practitioners had better knee muscle strength, less body sway in perturbed single-leg stance, and greater balance confidence. Significant correlations among these three measures uncover the importance of knee muscle strength and balance control during perturbed single-leg stance in older adults” balance confidence in their daily activities.