Context: Kinesio tape (KT) is a widely used intervention in the fields of sports and rehabilitation. However, its effects on lower-extremity behavior during functional activities are not entirely known. Objective: To test the hypothesis that application of KT can change performance and vertical stiffness (VS) during the countermovement jump (CMJ) before and after a fatigue protocol. Design: A predesign and postdesign to study the effect of KT in 2 situations, prefatigue and postfatigue. In each fatiguing condition, there were 2 conditions with and without KT application on the gastrocnemius muscle. Setting: Biomechanics laboratory. Participants: Fifty healthy, nonathlete participants (26 females and 24 males). Interventions: KT application on the gastrocnemius muscle and a fatigue protocol to induce fatigue in plantar flexor muscles. Main Outcome Measures: Various jumping parameters, including jump height, maximum force, maximum power, rate of force development, eccentric lower-limb stiffness, and VS, were calculated using the vertical ground reaction force data. Eccentric lower-limb stiffness and VS were calculated using a mass-spring model. The studied variables can present lower-extremity elastic behavior and performance during CMJ. Results: The results of a 2-way repeated-measures analysis of variance showed no significant effect for KT application. Fatigue resulted in lower values of jump height, maximum power, and VS. Moreover, male subjects showed greater values of jump height, maximum force, and maximum power than did females. Conclusions: The main finding of this study was that gastrocnemius KT has no effect on performance or elastic behavior of the lower-extremity during CMJ. Moreover, KT cannot reduce the adverse effect of fatigue in a functional activity such as CMJ. It seems that gastrocnemius KT is not effective for demanding activities.