The Social Identity Approach (SIA; Tafjel & Turner, 1979) provides an informative theoretical framework to understand and test how team identification can influence youth moral development. Based on the tenets of SIA and previous research, higher team identification is generally associated with adaptive behaviour toward in-group team members. This study examined the association of team identification on participants' pro-social and anti-social moral behaviour toward team members in a sample of 177 competitive youth soccer players (Mage= 14.66 years). Participants completed measures of social identity (team identification) and both pro-social and anti-social behaviour towards teammates during competition and in social situations. The Social Identity Questionnaire in Sport (SIQS; Bruner & Benson, 2018) examines three dimensions of team identification – in-group ties, in-group affect, and cognitive centrality – which were entered as individual predictors into a regression model testing the association with moral behaviour towards teammates during competition and in social situations. Regression analyses revealed in-group ties was significantly positively associated with pro-social behaviour in competition (β = .27) and in-group affect was significantly negatively associated with anti-social behaviour (competitive (β = - .30, and social (β = -.40; ps < .01). No social identity dimensions were significantly associated with pro-social behaviour in social situations. Overall, the results support the SIA and recent research (e.g., Bruner et al., 2018; McLaren et al., 2021) suggesting that a shared sense of social identity, in particular in-group ties and in-group affect, is associated with shared team goals and values (e.g., greater pro-social and reduced anti-social teammate interactions).