We aimed to investigate the effect of Taekwondo training on physical fitness, mood, sociality, and cognitive function among international students in South Korea. We randomly assigned 24 international students to a control group (CG, n = 12) and experimental group (EG, n = 12). The EG performed Taekwondo training for 16 weeks, while the CG did not train. Each participant underwent a physical fitness test and sociability questionnaire before and after the intervention. We also examined changes in mood state and cognitive function, using the Korean version of the Profile of Mood State-Brief (K-POMS-B), and the Stroop Color and Word test, respectively. Regarding the physical fitness variables, sit-and-reach records in the EG significantly increased after intervention (p < 0.05). In the sub-variable of K-POMS-B, Vigor-Activity scores significantly increased (p < 0.05) after intervention, while the Fatigue-Inertia scores significantly decreased in the EG (p < 0.05). Furthermore, in the EG, peer relationship scores, a sub-variable of sociability, significantly decreased after intervention (p < 0.05). These findings suggest that Taekwondo training can not only improve flexibility among physical fitness factors, but can also be effective in improving the mood state and sociality of international students.