Introduction ITF Taekwon-do is a kind of combat sports involving large number of kicks; it requires rapid and forceful kicking. Detailed analysis of Taekwon-do techniques is important for mastering the art. The aim of this study is investigation of biomechanical structure of roundhouse kick with front leg in Taekwon-do ITF. Materials and methods In order to better understand structure of kicks there were analysed papers on studies of karate, taekwon-do WTF, kickboxing and football kicks. 10 taekwon-do athletes (age: 12-14 years, height: 150-162 cm, weight: 38-52 kg; experience in sports: 3-5 years), with blue and green-belt levels participated in our study. Athletes performed roundhouse kick with front leg two times. Motion capture was done with two high-speed "Basler" cameras (100 Hz), data were processed with "SIMI motion” software. Results Taekwon-do kick consists of four phases – preparatory-, kicking-, contact with the target- and recuperation phase. In preparatory phase athlete performs a slight knee flexion and extension. Kicking phase (lasts in average 0.34 s) consists of two sub-phases - 1) Initiatory sub-phase (average 0.23 s), consists of: – foot take-off from the ground (average 0.08 s). The thigh and shank turn inwards (?) with knee flexion till toe takes-off the ground; – knee flexion (average 0.15 s). Flexion continues with hip flexion and inward rotation knee joint flexes to 82.45 ± 0.79 °. At the end of the motion hip, knee and ankle are in one plane parallel to the floor; 2) Kick execution sub-phase (average 0.11 s) lasts till the leg hits the target. Thigh inward rotation continues with knee extension. Target contact (average 0.08 s). Foot stays in contact with the target until drawn back. Knee reaches full extension. Then it starts flexion with hip extending. Recuperation phase (average 0.64 s). After target contact leg moves backward repeating kicking trajectory till foot touches the ground. Conclusions The front-leg roundhouse kick in Taekwon-do for 12-14 year-old athletes (excluding preparatory phase) lasts in average 1.06 s and consists of four phases – preparatory-, kicking- (average 0.34 s), target contact- (average 0.08 s) and recuperation phase (average 0.64 s). In the preparatory phase athlete prepares to kick and slightly bends a knee. Kicking phase consists of initiatory sub-phase (hip and knee flexion and inward rotation) and kick execution sub-phase (hip flexion and knee extension). After contact with the target leg speed decreases, foot remains in contact with the target for about 0.08 s. During recuperation phase leg follows the same trajectory as during kicking phase.