While research exists to induce fatigue using isokinetic dynamometers or simple repetition tasks in patients with chronic ankle instability (CAI), there is a lack of research examining landing movement strategies using fatigue protocols that mimic actual sports. Therefore, we aimed to investigate the effects of CAI and fatiguing exercises on the lower-extremity kinematics and kinetics during single-leg drop landings among patients with CAI, lateral ankle sprain (LAS) copers and controls. A cross-sectional study recruited 20 patients with CAI, 20 LAS copers, and 20 controls in a biomechanics laboratory. All participants performed single-leg drop landings before and after the fatiguing exercises. The fatiguing exercise protocol consisted of a cycle including forward, side, and backward running, L-shape running, side hopping, cone jumps, and tuck jumps. This cycle was repeated until rate of perceived exertion (RPE) reached 17 and heart rate (HR) reached 85% of the maximum. Three-dimensional kinematics and kinetics of the lower extremity were collected and analyzed using functional analysis of variance. All participants reached an RPE level of 17.89 ± 1.02 and HR of 180.64 ± 7.87 (maximal HR 96.11%) at the last cycle of the fatigue protocol. Several group-by-fatigue interactions were noted. Patients with CAI exhibited increased hip external rotation angle and moment, increased angle and decreased moment of knee valgus, and increased hip and knee extension moments after the fatiguing exercise compared with copers and/or controls. Under fatigue conditions, patients with CAI exhibited biomechanical changes in the proximal joint, a stiffer landing position, and biomechanics associated with ankle injuries. Fatigue resistance training should be a key focus during the rehabilitation of these patients to improve their lower-extremity stability.