Background: Mental fatigue can impact physical demands and tactical behavior in sport-related contexts. Small-sided games are often used to develop a specific sport-related context. However, the effects of mental fatigue on physical demands and tactical behaviors during soccer SSGs have not been aggregated for systematical assessment.Objective: This systematic review was conducted to compare the effects of mental fatigue vs. control conditions in terms of the total running distance and tactical behavior of soccer players during SSGs.Methods: The data sources utilized were (...) PubMed, PsycINFO, Scielo, Scopus, SPORTDiscus, and Web of Science. The study eligibility criteria were established based on PICOS: Population: healthy youth and young adult men soccer players with regular training practice and belonging to teams with regular competitions; Intervention: exposed to mental fatigue-induced protocols only before SSGs; Comparator: control conditions before SSGs; Outcomes: physical demands and tactical behavior ; Study design: counterbalanced cross-over design; and only full-text and original articles written in English.Results: The database search initially identified 111 titles. From those, six articles were eligible for the systematic review and meta-analysis. Results showed no significant effect of fatigue on total running distance and tactical behavior.Conclusions: A non-significant effect of mental fatigue on total running distance and tactical behaviors performed by soccer players during SSGs was found in this systematic review. (shrink)