Introduction: Small-sided games (SSG) are used as training tools for physical conditioning in soccer. To date, however, it is unknown whether team composition affects athletes' physical performance. Specifically, based on the differences presented by players of different positions, it is expected that the use of positional status as a criterion for team composition will affect players' physical performance. Objective: To compare the physical demands of SSG in teams composed of young soccer players in the same position or different positions. Methods: 12 U-15 soccer players participated in the study. The athletes performed 3v3 SSGs under two conditions: teams in which the athletes played in the same position (i.e. three defenders), and teams in which the players took up different positions (i.e. defender, midfielder and attacker). Data were obtained on total distance traveled, distance in speed zones, and accelerations, using GPS devices. The data were analyzed using the paired t-test, comparing the two experimental conditions. Results: There was higher physical demand among defenders and midfielders when the SSG was performed with athletes playing in the same position, in terms of distances covered in different speed zones. However, there were no differences in relation to acceleration actions. Conclusion: Team composition affects the physical performance of soccer athletes during 3v3 SSG.