The aim of this study was to investigate the relationship between sources of social support and motivation and the moderating effect of gender on this relationship for physical activity participation in adolescents. In this study, the relational screening model, one of the quantitative research method, was used. The research was carried out in accordance with the cross-sectional survey design. The data obtained were evaluated by SPSS 21.0. The research data were obtained from a total of 670 adolescents who were selected by convenience sampling method among secondary and high school students in Ankara, Bursa and Istanbul. As a data collection tool, the Physical Activity Participation Motivation Scale (PAPMS) developed by Tekkursun Demir and Cicioglu (2018) and consisted of 16 items and 3 sub-dimensions, was used. In order to determine the social support perceptions in physical activities of the students in the research, Social Support Scale for Physical Activity in Adolescents (SSSPA) which was developed by Farias Junior et al. (2014) and adapted to Turkish language by Küçükibis and Eskiler (2019) and consisted of 10 items and 2 sub-dimensions, was used. Our findings demonstrated that there was a positive relationship between physical activity participation and participants' motivation in physical activity and their perceptions of parent and peer social support. Additionally, there was no statistically significant effect of gender interaction with perception of parental social support on physical activity participation motivation (t=1.36, p>0.05). However, it was identified that peer social support perception and gender interaction had statistically significant effect on physical activity motivation (t=1.99, p<0.05). The results indicate that as the perception of parent and peer social support increases, female students' motivation to participate in physical activities increases more than male students. In other words, female students were more positively affected by parent and peer social support than male students. Consequently, adolescents' social support for physical activities had positive effects on their participation and motivation.